I actually disagree with the notion that the US pays for the graduate educations of foreign nationals. This is a misconception that is easy to exploit in a population that thinks of graduate school as something like undergraduate, law, business, or medical school.

Graduate students in engineering are generally producers of wealth for universities. For example, I recently left a job where I was paid over 100K a year (in addition to benefits and stock) to write code that built mathematical optimization models based on data stored in large RDBMSs. Now, I don't actually think the pay was especially great considering the skill set (and I got a hefty raise when I left), but I know foreign grad students who were doing essentially the same thing for a research stipend that probably amounted to less than 20K/year, no benefits, stock, nothing (other than the possibility of a PhD after many years of servitude). If these folks had the right to leave the university without screwing up their visas, they'd probably be making six figures in private industry like me (I left once I got my MS).

Sure, yeah, I suppose we should try to keep these folks here when they graduate, but the notion that the US has somehow put itself out to provide a grad education for foreign engineering students is baloney. We take them in precisely at the moment they become net contributors, and not a moment earlier. Universities save huge $$$ by indenturing grad students from overseas.