The Republican party is far from broke, so I'd say "many". Example: the Koch brothers. They're not very much upvoted on Reddit or HN though, and generally don't use social networks a lot, so we don't hear about them as much. They don't need popularity anyway: they have money.

Bill Gates is one of the few who really seems to want to give back, so we read about him a lot. It's a better news story than "Shocking! Another Rich Guy Turns Out to be Greedy" or "Wealthy Person Still Not Giving a Lot of Money".