But is wealth really material or is it mostly virtual? Musk may be one of the richest men on Earth but he doesn't have a Trillion in his bank account. He holds stock which is potentially worth that amount. But as soon as he were to sell it the price and value would sink and it would be worth much much less. How much less? I don't know exactly but I suspect at least half.

So maybe we should take into account the liquidity of the assets held by these Billionaires. Also, as we've seen with Steve Jobs that if you get cancer it doesn't really matter how much you have in the bank. You'll die the same just like everyone else. All that money won't buy you extra time.