I don't disagree on all of these points, but I will say that I am currently in grad school in a Top 100 MBA program, and the Asian students are quite active on campus and not self-segregating at all. Oddly, I found that to be more common in my undergrad experience at an Ivy League school. Still, international students with brains and/or means come to the United States in droves. It's not because they want to dick around in the States for a few years.2) Many people from other countries come to the US to study for a variety of reasons... one being "brand recognition" in their home country (that is related more to a school's marketing campaign), the opportunity to improve their English, and just wanting an experience abroad. I wouldn't say that it is entirely because the US has the best higher education, even if this is the case. However, these international students come from exceptionally prosperous background, and oftentimes US universities treat them as full tuition-paying cash cows (just to be able to enter most schools require of international students proof of a certain minimum in your bank account). It is not as meritocratic an admissions system for them as it is for domestic students, so it's a stretch to say that their presence increases the quality of learning. And... I am currently doing research on the dynamics of social integration on campus, because there is not much evidence that the presence of international students necessarily adds to "diversity" as they are often self-clustered in their own groups.
That speaks to improving standards in Asian universities rather than decreasing standards in the U.S., though, doesn't it?3) Interestingly study abroad patterns are changing. The US still receives the most international students, but the rate of growth has slowed in recent years. International students in the US mostly come from Asia; now there is much more intra-region Asian study abroad (with China's growth rate of incoming international students skyrocketing).