He made his billions by being a contrarian: "be greedy when others are fearful" and "be fearful when others are greedy."
He became the second richest man in the world, and he knows that you can't take it with you.
However, I think that Ted Turner started these billion dollar donations a few years back. What came afterward was, probably, charity one-upmanship.
Hopefully, other billionaires and millionaires will follow his lead.
The Warren Buffet News Story