I have a different take on this.
It has nothing to do with a cultural shift. I dont care where you go in the world, culture in particular is very difficult to stamp out. It shapes the way we interact and view things. Its why sub culture is so prevalent in the west where society tends to be more multicultural. You find you start to identify with a culture more the longer you are there, but everything about you will be different. No amount of time in a new country will change that.
The answer here is a lot simpler then most men realise. Foreign women are not "infected" by the local culture. Their VALUE skyrockets when they go to the USA. They have a larger pool of high quality men to choose from and as a result become more demanding.
The reason why American men do well overseas is because they have more to offer as men when compared to the locals. Not that the local men are that bad, its just that they cannot provide for them in the same way you can. And they are in short supply.
You are considered wealthy if you can travel. The fact that you hold down a job and actually go to work is a big plus. The fact that you wont beat the crap out of her when she gets lippy is another bonus. The fact that you tend to be more faithful (even though you have so many options) is another tick in the box. So she will do everything she can to keep you.
Take her to the USA and the roles are reversed. There are not 100 other beautiful, 20 year old women chasing you. There are men in abundance, and they can all provide for her in much the same way you can. The laws are so skewed just a claim of abuse gets you a night in jail. Not only are there fewer women chasing you, there are fewer women who can compete with her. Most of them are fat and lack the femininity she has. Throw into the mix the anti male attitude in the west and you have the proverbial kid in the candy store.
There is a shift in value Im afraid and it has little to do with the local culture. In her country, you are a prize catch. In your country, she is a prize catch. When it is in a womans nature to trade up, many will act on it.
Now, in saying that, according to wiki almost 80% of mail order marriages are successful. Only 20% end in failure. Considering that marrying an American women leads to a 1/2 shot of divorce, the odds are in your favour anyway. Chances are, the majority of those men in that 20% bracket were losers and morons anyway.