[doosra]

While only speaking from experience, I've noticed that many foreign PhDs in CS, Electrical and other engineering fields are increasingly electing to go back once they are done.

The main reasons seem to include being so far away from family and being in an alien culture. Further, jobs for PhDs are increasingly available in their home countries-- this seems to seal the deal. The tough immigration stance contributes to the discouragement since foreign workers have to "pause" their lives until they get their green card.