[kqr]

According to whom? The research I've seen on this confirms Bernoulli's intuition that happiness scales with the logarithm of income.

Sure, the logarithm is slowly varying in the limit, but that seems like a very unusual definition of both "beyond some amount" and "absolute amount stops mattering."

[lex-lightning]

The logarithmic decay could be more about more and more people hitting their satisfaction level, than about what the wealth can purchase. In other words, very few people actually want to be billionaires.

Or more simply: most people want to retire.