Bill Gates was a college dropout too - funny thing about some of these guys. They create their own business without an overpriced college degree that's only awarded after they spend 4-6 years and tens of thousands of dollars taking classes in which half are dedicated to irrelevant subject matter...but that's for another thread.
However - Buffett, Gates, Jobs et al don't pay significant income taxes every year because they've already accumulated their wealth and during that process their taxes were already assessed significantly. Why should their wealth be taxed again - essentially confiscated by the government?
If Warren Buffett is consumed with guilt due to his success in business, he can always donate the millions he doesn't need to the US Treasury - to be promptly wasted by nameless, faceless bureaucrats. Maybe his grandchildren need to take him on a nice trip around the world to occupy his time for the next 14 months.