But this is just a generalization. There are many American women who are gold diggers as well.
American woman are less complicated because they grew up in a less competitive world in terms of survival and life style.
Another factor that can not be igored is religion. Half of American women were brought up in the evangelical environment, their value system is a little different from those who were brought up in a materialist society like China.
Last but not the least, don't forget that there was big swings of social norms in the US. Remember what they say about the sixties? The pendulum of Chinese value just reached one extreme about now, it will swing back sometime in the future.