[ktizo]

Doesn't really matter how long a specific rich individual lives for this to work. As long as there is a culture of rich people doing it, then things would average out. Especially given that the life spans of very rich people tend to be longer.

[Schwolop]

To an extent this was my point too - if a decent number of people do this, then the few who get mega-rich and become philanthropic will make up for the many who fail to get mega-rich, and also the few who get mega-rich but don't become philanthropic. Well... hopefully!