The US system is different. Top colleges do not give out places simply based on a set of test scores (which, in my honest opinion, discriminates far more on class and race than the US system does). The US system rewards accomplishment. Accomplished asians obtain ivy league places. Accomplished whites do. Accomplished hispanics do. There's absolutely no question about that.
The problem that has been discussed is that asians with higher scores are equally likely to obtain places as black and hispanic students with lower scores. First of all, I'll say this - the cut off for the top 1% on the SAT is about 2200. Almost every african american and hispanic student I've met here had obtained a score above that limit. The differences in the scores might appear to be large, looking at the SAT score differences, but really, they're not that big in terms of percentiles.
And it's not about hard work being ingrained into asian (and, as I said, white middle class - heck, I'm white and middle class, and I admit it) culture. It's that this hard work leads to high test scores, which aren't the best metrics of achievement. In many cases, the emphasis on scores leaves little time to devote to doing other things. I'm going to be completely blunt and say that most people I know who scored high ATARs- white, asian or otherwise - would not have nearly the right accomplishments to stand out at these schools. Sure, you can get 99.95 and a bit of community service and some school clubs, but I honestly don't think that an asian or a white student with those scores is more deserving than a black student with a 99.00 who's also founded a business and been recognized on national television for being an entrepreneur, or even an asian student who scored 99.50 and has worked as a professional journalist (and yes, I know people who basically fit those categories). I feel inadequate about what I've done with my life, and I did well within the realm of things academically in Australia (IPhO, APhO, 99.95, writing/french competitions...).
To basically sum up everything, asian students and middle class white students tend to have higher test scores, but that doesn't mean that they're more accomplished or that they have more potential.
Sigh I hope I've tried to explain this well enough.