I think Asian is the one main exception to that rule, just as it's the exception when it comes to minorities in elite colleges.

Asian Americans don't have as much of a history of economic and political oppression (There was some, obviously, especially during WWII.), and the culture strongly encourages working hard to excel at school, helping them then get good educations and break out of the initial poverty cycles that formed when Asians first came over and were exploited by railroad companies and the like.

But if you look at startups for other minorities--Hispanics, African Americans--I think it is pretty true that they are not well-represented.

I have no idea about the situation in the US but could this be due to other factors? For instance, you mention that these minorities are under represented in certain colleges to begin with - a place where a lot of startups begin. Perhaps there is less internet exposure too, or at least to the startup community blogs etc.. And maybe it just comes down to a perpetuating loop situation. In any case, and I don't really know US attitudes, but I would doubt in this day and age there is a conscious effort among hackers, who are generally more liberty and equality focused anyway, to exclude people based on anything other than merit.

According to the stats posted below disproportionate to the tune of 50%.