[HarryHirsch]

To keep down wages, why else? If you have the choice between an American, who can leave for a better-paid opportunity whenever he likes, and a foreigner, who is chained to his job because of the green card process, who would you hire?

There is the additional twist that an immigrant foreigner who got their degree abroad won't nearly be as encumbered by student loans as someone with a domestic degree and won't negotiate quite as hard for a higher salary.