Bill Gates is an optimist. He believes the world will be a better place in 20 years, that diseases like polio, measles and malaria will be eradicated, and that there will be other rich people lining up to fill the void when, as he announced recently, his foundation shuts its doors in 2045. Of all these audacious goals and wishes, it's the last that might be the furthest out of reach. Gates is right that there will be plenty of rich people in two decades. But what's far less certain is just how willing they'll be to give away their money with the abandon and largess shown by Gates, demonstrating how the norms of billionaire philanthropy have shifted.

The announcement that the Gates Foundation will close in 20 years came on the heels of news that Warren Buffett will soon retire as CEO of Berkshire Hathaway Inc., creating a distinct "end of an era" vibe for this variety of billionaire philanthropy. It was Buffett who introduced Gates to the idea of giving it all away, and together they've convinced and cajoled plenty of other billionaires to do the same. In 2010, they announced the Giving Pledge, in which hundreds of the world's richest people have committed to giving away half of their money, ushering in an amped up "with great wealth comes great responsibility" paradigm. (Michael Bloomberg, the founder and majority owner of Bloomberg LP, is a Giving Pledge signatory and his philanthropic organization has worked with the Gates Foundation.)

Today that idea seems to be falling out of favor. In its place, a new model is bubbling up, driven by a subset of the Silicon Valley elite. It goes something like this: Why donate your money when you've already given so much to society through the technology you've created? Gates and Buffett felt they were returning something to a system that had allowed them to amass such wealth; the new guard believes it's already contributed more to the system than it will ever get back in return.

Read the full article about billionaire philanthropy by Beth Kowitt at Miami Herald.