If you look at most decent engineering universities, are they any different if you restrict to engineering/science departments? I don't have statistics, but when I was in grad school, the mini-institute I was part of (5-6 faculty members + students) had more than 70% foreigners. And I think all the non-foreigners were born abroad (whether Green Card or US citizen).

In my very average undergrad university, the EE department had 2 American PhD students, and something like 6-10 international students.