But the vast majority of people, in America, in Europe, and in South Asia and Africa, want MORE STUFF. That's how they measure personal happiness. That's the sad fact, and until you figure out how to change it, the PPP per-capita GNP figure is the most accurate way to measure what people want.

GNP has very little to do with the power of "the people" to buy stuff. That is the point. It's a crap way of measuring what you suggested: Migeru suggested that, if you want to measure the ability of people to buy stuff then median income, PPP adjusted, is a good metric.