There comes a point at which marginal wealth stops having much utility, other than as a metric to compare yourself to others.
Steve Jobs's behavior provides a decent demonstration of this. He was okay taking a $1 salary because it cast him as the great CEO taking a hit for his company. But when the board insisted on paying him, he told them their offer was too low. He wanted to be _either_ the great sacrificing CEO or the great CEO who is equally well-compensated, because he didn't actually need the money, but he wanted the reputation from it.
If it's just being used as a yardstick anyway, we might as well tax most of it.