Undine- Ralph Marvell marriage and the custom of the country

The Undine- Ralph Marvell marriage very much reminds me of the Lydgate- Rosamond marriage in Middlemarch. The similarities are probably deliberate. In both cases, the man is a decent man but has a narrow, mistaken view on women; he marries a beautiful woman he idealises, but at the same time also looks down on her; she turns out to be selfish, shallow, and incompatible with him, and because he treats her like a child and keeps things from her, she doesn’t understand anything and brings him to his ruin. 
Another strong similarity between Rosamond Vincy and Undine Spragg is that both of them never think they’re wrong. They’re incapable of recognising and acknowledging their own fault—there’s always someone else to blame. 
Chapter 15 of The Custom of the Country has an interesting discussion between Laura Fairford (Ralph Marvell’s sister) and her friend Charles Bowen. 

“He paused. "The fact that the average American looks down on his wife."
Mrs. Fairford was up with a spring. "If that's where paradox lands you!"
Bowen mildly stood his ground. "Well—doesn't he prove it? How much does he let her share in the real business of life? How much does he rely on her judgment and help in the conduct of serious affairs? Take Ralph for instance—you say his wife's extravagance forces him to work too hard; but that's not what's wrong. It's normal for a man to work hard for a woman—what's abnormal is his not caring to tell her anything about it."
"To tell Undine? She'd be bored to death if he did!"
"Just so; she'd even feel aggrieved. But why? Because it's against the custom of the country. And whose fault is that? The man's again—I don't mean Ralph I mean the genus he belongs to: homo sapiens, Americanus. Why haven't we taught our women to take an interest in our work? Simply because we don't take enough interest in them."” 

Note the appearance of the book’s title (my emphasis).
Blah blah blah, then: 

“"Yes; and the most indifferent: there's the point. The 'slaving's' no argument against the indifference. To slave for women is part of the old American tradition; lots of people give their lives for dogmas they've ceased to believe in. Then again, in this country the passion for making money has preceded the knowing how to spend it, and the American man lavishes his fortune on his wife because he doesn't know what else to do with it."
[…] Bowen paused to light another cigarette, and then took up his theme. "Isn't that the key to our easy divorces? If we cared for women in the old barbarous possessive way do you suppose we'd give them up as readily as we do? The real paradox is the fact that the men who make, materially, the biggest sacrifices for their women, should do least for them ideally and romantically. And what's the result—how do the women avenge themselves? All my sympathy's with them, poor deluded dears, when I see their fallacious little attempt to trick out the leavings tossed them by the preoccupied male—the money and the motors and the clothes—and pretend to themselves and each other that THAT'S what really constitutes life! Oh, I know what you're going to say—it's less and less of a pretense with them, I grant you; they're more and more succumbing to the force of the suggestion; but here and there I fancy there's one who still sees through the humbug, and knows that money and motors and clothes are simply the big bribe she's paid for keeping out of some man's way!"” 

(The discussion is longer, but I’ve kept a large part of it). 
Is this Edith Wharton’s view? I don’t remember Charles Bowen ever opening his mouth before. If this is Wharton’s way of commenting on the marriage and the American way, it is subtler than, you know, George Eliot.  
In a way, it’s true. Undine is mercenary, but she doesn’t think about money in itself, but about comfort, luxury, extravagance, and distinction. She doesn’t understand the value of money, and doesn’t care where it comes from—all she cares about is getting “the best”. That is the way Mr Spragg raises her: 

“All his life, and at ever-diminishing intervals, Mr. Spragg had been called on by his womenkind to "see what he could do"; and the seeing had almost always resulted as they wished. Undine did not have to send back her ring, and in her state of trance-like happiness she hardly asked by what means her path had been smoothed, but merely accepted her mother's assurance that "father had fixed everything all right."” (Ch.10) 

It is, in fact, the way Mr Spragg treats his wife as well as his daughter. 

“He had been "seeing" now for an arduous fortnight; and the strain on his vision had resulted in a state of tension such as he had not undergone since the epic days of the Pure Water Move at Apex. It was not his habit to impart his fears to Mrs. Spragg and Undine, and they continued the bridal preparations, secure in their invariable experience that, once "father" had been convinced of the impossibility of evading their demands, he might be trusted to satisfy them by means with which his womenkind need not concern themselves.” (ibid.) 

Both Mrs Spragg and Undine have no understanding of money and the difficulty in getting it, so when Undine wants something, they gang up on him. 
Look at the scene where she asks him to get her an opera box. 

“Mr. Spragg's brow remained unrelenting.
"Do you know what a box costs?"
"No; but I s'pose you do," Undine returned with unconscious flippancy.
"I do. That's the trouble. Why won't seats do you?"
"Mabel could buy seats for herself."” (Ch.4) 

She doesn’t care how much it costs—she wants it, and she will get it. 

“"A parterre box costs a hundred and twenty-five dollars a night," saidMr. Spragg, transferring a toothpick to his waistcoat pocket.
"I only want it once."” (ibid.) 

But even when she knows the cost, she doesn’t know what it means. The amount is abstract and meaningless to someone who never works and never handles money. This is an important scene because it says everything you need to know about Undine, and also explains why she is the way she is—her family spoil her rotten.

“Undine hated "scenes": she was essentially peace-loving, and would have preferred to live on terms of unbroken harmony with her parents. But she could not help it if they were unreasonable. Ever since she could remember there had been "fusses" about money; yet she and her mother had always got what they wanted, apparently without lasting detriment to the family fortunes. It was therefore natural to conclude that there were ample funds to draw upon, and that Mr. Spragg's occasional resistances were merely due to an imperfect understanding of what constituted the necessities of life.” (ibid.)  

It is no wonder that later on when Ralph and Undine are in Europe and need to return home for lack of funds, she neither wants to sail within the week and lose her fun, nor wants to leave later in an uncomfortable slow boat. She has to have it both ways, she has to have the best, and Ralph yields as he can’t make her understand. 
There is no doubt that Ralph is the victim in the marriage and Undine is an opportunistic, selfish, and manipulative woman, incapable of empathy and self-reflection. It’s understandable as well that Ralph looks down on her—after all, she is shallow, ignorant, and a philistine, having no sensibilities for art, literature, music, or nature. Undine not only has no principle but also lacks a sense of self—she is hollow and imitative. 
But Edith Wharton also forces the readers to see another aspect of their marriage—Ralph looks down on Undine, and does nothing to help her improve herself nor engage her in “the business of life”. 

“[Mrs Shallum] saw at once Undine's value as a factor in her scheme, and the two formed an alliance on which Ralph refrained from shedding the cold light of depreciation. It was a point of honour with him not to seem to disdain any of Undine's amusements […] With her quick perceptions and adaptabilities she would soon learn to care more about the quality of the reflecting surface; and meanwhile no criticism of his should mar her pleasure.” (Ch.12) 

And: 

“Undine's moods still infected him, and when she was happy he felt an answering lightness. Even when her amusements were too primitive to be shared he could enjoy their reflection in her face. Only, as he looked back, he was struck by the evanescence, the lack of substance, in their moments of sympathy, and by the permanent marks left by each breach between them. Yet he still fancied that some day the balance might be reversed, and that as she acquired a finer sense of values the depths in her would find a voice.” (Ch.13) 

He naively thinks she can change, but does nothing to help her change. Just once he takes her to a play, which she’s too ignorant to appreciate, so afterwards he goes to the theatre alone and leaves her to do her things. 
Now look at it from Undine’s point of view: 

“[Mr Popple’s] conversation struck her as intellectual, and his eagerness to have her share his thoughts was in flattering contrast to Ralph's growing tendency to keep his to himself. Popple's homage seemed the, subtlest proof of what Ralph could have made of her if he had "really understood" her. It was but another step to ascribe all her past mistakes to the lack of such understanding; and the satisfaction derived from this thought had once impelled her to tell the artist that he alone knew how to rouse her 'higher self.'” (Ch.14) 

This doesn’t justify her selfishness and lack of empathy (she forgets her own son’s birthday!), but Wharton makes us consider the marriage from a different point of view. Let’s go back to Ralph before the proposal: 

“The clearness with which he judged the girl and himself seemed the surest proof that his feeling was more than a surface thrill. He was not blind to her crudity and her limitations, but they were a part of her grace and her persuasion. Diverse et ondoyante—so he had seen her from the first. But was not that merely the sign of a quicker response to the world's manifold appeal? […] the girl's very sensitiveness to new impressions, combined with her obvious lack of any sense of relative values, would make her an easy prey to the powers of folly.” (Ch.6) 

Ralph sees her crudity and limitations from the start, but chooses her anyway. He himself picks an intellectually inferior, incompatible wife.