Well, as every other generalization, that particular one too is false, if taken literally :)
But more to the point, if there is such a thing as a general statement that describes Eastern European immigration (I presume it may also be true of immigrants from other regions) is that the only difference that really matters is neither time nor political convictions, but gender. I do not think this issue received much attention, but men and women have much different stakes in immigration, those stakes change quite dramatically after migrating from the old country, and so do the attitudes toward the old country.
On the pain of oversimplification, men generally expect a better life in the new country. They often emigrate alone, leaving their families behind on the promise to fetch them after they make necessary arrangements. I do not have any stats, but based on anecdotal evidence that often does not happen, and man's emigration is often a de facto divorce without the need to pay child support or alimony.
Women, on the other hand, usually follow their husbands or boyfriends. I did not meet many single women emigrating on their own. After the initial period in the new country, when they literally serve as "comfort women" to their male companions to ease the discontents of adaptation to the new environment, two things usually happen. First, the "old country" wife is exchanged by her male companion for a newer model, but not necessarily of the foreign make. Second, the "old country" husband/boyfriend is dumped by the woman, but not necessarily exchanged for a newer model.
In each case, the woman is a big winner - because that development means shedding the "old country" patriarchal obligations (regardless of who does the dumping). The woman is lietarlly liberated to have her own money, her own time, her own style, and her own sex life is she so chooses - without being pressured to conform to societal expectations. I can cite numerous anecdoacl evidence to support that.
Consequently, women have fewer incentives to go back to the old country, even though they are often emotionally attached to it, and even though their material situation in the US may be worse than the one they left behind. That would mean giving up their newly attained freedom for the old patriarchal yoke.
Men by contrast, tend to go back if they see an opportunity (e.g. if they saved some money and can open a business in the old country) especially that old country patriarchy is often the added value to their material success. If they are less successful, e.g. if they sold their property in the old country but did not gain much in the new country, obviously going back would translate to a loss of status. Consequently they rationalize their decision to stay by fabricated images of horrors of the old country - persecution, misery, poverty, hopelessness, you name it.
A classiacl work on EE emigration is Thomas & Znaniecki, _The Polish Peasant in Europe and America_ (edited and abridged by Eli Zaretsky), Urbana and Chicago: University of Illinois Press, [1918-20] 1984, although they did not seem to pay much attention to gender issues. I do not think immigration has been extensively studied since then, let alone from a feminist perspective. Can any of our resident feminists correct or add anything to that?
Wojtek