I think there's more to it than net worth. There's the question of how much your money will buy in a particular place.
Let's also bear in mind that when you compare numbers for different countries, you're not comparing apples to apples as far as what the numbers mean in terms of lifestyle level. A so-called U.S. poverty-level income would be enough to live large in many other countries.
Come to think of it, even in the same country there are going to be great variations from area to area in the lifestyle that a certain income level can provide. Which is why there are such things as (relative) high cost of living areas and low cost of living areas.