Doesn't matter - it's not the quality of the students, it's the quality of the instruction. The universities that make all the money can also attract and pay the best instructors. That does not mean that there are not excellent instructors at every level, in all sorts of settings, but when money is involved, you can indeed buy the best and that's what the richest universities do.
The top-end universities can also afford to buy the best equipment and fund the best working environments if you're talking about hard sciences and so on which require things like particle accelerators and whiz-bang gadgets. So again, this has the synergistic effect of attracting the top-end teaching talent, the best post-grad type students, and even the best research grants and outside-funded experiments. Let's face it, the USA has a stranglehold on this.
Changing? Yes, it is changing. I do not argue with those who say that China is on the rise. I am also quite aware of the fact that we do not have as many post-grad hard sciences students in our own universities as we do those from other countries. They come here, learn from us, and go home; we lose brain power yearly. However, if Americans want to sit in front of the TV and watch the game and drink beer, so be it.
For the moment though, the USA still rules the education game. We're the smartest, and by a lot.