@aral: This is a natural outcome of loose marginal tax rates at the high end of income. Levying high taxes on the rich is prosocial, in part, because it gives the zillionaires a motive to re-invest that income, and to spend it in ways that zillionaires are known to like but aren't taxable, such as naming museums after themselves. By taking that motivation out of the equation, the sort of people primarily motivated by hoarding money get a strong advantage at the money-hoarding game.