I was under the impression that AA applied to college admissions, and that college graduation is still entirely contingent on one's performance. (Though I've heard tell that legacy students both get an AA-sized bump to admissions and tend to be graded on a much less harsh scale.)
A quick google search isn't giving me an actual percentage, but I believe that students who're admitted to and attend college, but do not graduate, are still significantly in the minority. Even those who barely made it in mostly graduate, if not necessarily with good GPAs.
One of the criticisms of colleges engaging in "AA" type policies is that they often will put someone in a slightly higher level school (say Berkeley rather than Davis) than they really should be in and which because of their background they are unprepared for. Not necessarily intellectually--they could be very bright, but in terms of things like study skills and the like.
There is sufficient data to suggest this should be looked at more thoroughly. In general it is better for someone to graduate from a "lesser" school than to drop out of a better one.
Here's the new thread for posting quotes, with the usual rules: