I find it really hard to take these lists seriously.

How many billionaires (or even millionaires that you know) keep the fact close to their chest? There's probably a lot of quite rich people out there who are more than happy to let you think someone else is richer than them.

Keeps the vultures and losers away from them and lets them get on with enjoying life.

In fact I'm certain there's quite a few people to go to extensive lengths to stay OUT of lists like this.

EDIT: Oh and paper money does not count until you execute your trade. Just ask anyone who was "rich" before the crash.