There's also the fact that a lot of foreign applicants completely fabricate their credentials, with the full buy-in from the institutions that churned out their degrees. So while there will be some applicants who graduated from top tier schools, there will also be a lot who graduated from the equivalent of DeVry who have fantastic resumes that are full of BS. And you won't find that out until long after you've hired him.
I wonder if this practice is also influencing the "requirements bloating" that happens in HR departments. Fake resumes get turned in that have all these fabulous sounding things, so they plop them into the job requirements - if some resumes have them, that means some applicants should have them too! Next thing you know they want someone with 10 years experience with Ruby on Rails.