The problem with Gini index is the definition and data being used to compile the chart. For example, in the US, if you use taxable income as a metric, then you miss out on a load of deductions that we use to lower our tax burden. Shek put up a chart on the US
consumption rather than income to better illustrate the equality, or inequality, of the population.
You Are What You Spend
The lowest 20% of US household has an average income of $10000, but an average consumption of $18000+. Interesting, isn't it?