Billions over billions
Does it actually matter whether you have 35 or 40 or 50 billion sitting somewhere? Unless you play the game of "mine's bigger than your's" and are not planning on buying entire countries, there is nothing that you couldn't do with 35 that you can do with 50 billion, right?
In the end, money is what money does. In Germany we have a saying "your last shirt doesn't have any pockets". So, what's the use of piling up the billions? When you leave this planet, you cannot take it with you anyways.
I strongly believe that for William Gates III. money is not the important issue here. It is more about power, competitive edge and turning visions into reality (every desktop/notebook running MS products...).