One difference is that billionaires (at least the Buffett / Gates crowd) seem to put a lot more of their donations toward projects in foreign countries than the

One difference is that billionaires (at least the Buffett / Gates crowd) seem to put a lot more of their donations toward projects in foreign countries than the government would. Since the vast majority of people living in bad situations in the world are not Americans, I think it's very plausible that they're doing more good with the money than we would get from taxing it.