People emigrate for many different reasons. The U.S. does have policies which privilege professional and more highly skilled emigrants. "Skimming" is perhaps an apt description. 
But there are many people who come to the U.S. just for work, to support families back home, to make it possible to build a house, back home. Their remittances and general commitment to their native countries are significant. But maybe there are not very many Doctors and tech workers among them.

The better-off generally gravitate towards enclaves of privilege. Suburbs, genteel neighborhoods, and jealously guarded schools. We can see, right here, the effects of "skimming" when we consider the disparate qualities of public schools, municipal services, and commercial enterprise. I think what you are describing is the privilege of relative wealth. Very few do not avail themselves as they are able, whatever it may cost their neighbor. It's a worthy concern in our own populace, as well as for other nations.