Cool? I found it confusing. Not to mention there are clear rendering problems with the fonts (not just in my browser, but in the original if you look at the Wikipedia PNG equivalents). I think the diagram needs "Tufte attention".
It helps if you understand Gini coefficients. But in short, they attempt to represent wealth distribution as a scalar from 0 to 1, where 0 is a uniform homogeneous distribution.
So to read the chart, you can tell how big the pie is by how long the bar is, and the non-uniformity in the distribution by how toppled the bar is.