When Buffet gave that money away back in 2006, he gave away $36 billion dollars, kept $9 billion. Said why would you need more than that at his age (at the time about 80). In the last 4 years, he's made more money back than what he gave away, so now he's richer than what he was then
Once you've got that much money, making even more is all too easy. You don't even have to do anything to make the money!!!.