re: Skewness
The U.S. is pretty much in the middle of the wealth distribution curve. Few other places on the planet have "the lower classes" doing as well as they're doing here.
Differences in national income equality around the world as measured by the national Gini coefficient. The Gini coefficient is a number between 0 and 1, where 0 corresponds with perfect equality (where everyone has the same income) and 1 corresponds with perfect inequality (where one person has all the income, and everyone else has zero income). Countries in red tones have societies with more income inequality than those in green tones.
From Wikipedia
Not sure why the Middle Eastern oil nations are largely left out of the chart. I found Japan's color interesting.