Guys like Buffet, Murdoch, Bloomberg, Carlos Slim, etc don't retire. Some may redirect their efforts, but that's the point. The most ambitious continue building their empires.
I wonder at what point the world's richest will no longer include those philanthropically inclined like Buffet, Gates, and Bloomberg and will be dominated by the likes of Bezos, Slim, and Ortega. (The jury is still out on Zuckerberg and his dubious initiatives)
Our global economy is trending towards benefiting only the most ruthless, even at the very top.