It includes people who have filed a tax return and also this number is skewed against the top earners because "Readers should note the IRS dataset excludes the refundable portion of tax credits such as the earned income tax credit, which means the IRS data overstates the tax rate paid by taxpayers at the bottom.".

I do understand it, better then you do.

The US tax polices are some of the most progressive in the world and although we don't have some of the same exact social programs some of the Europeans have we also don't have the regressive consumption taxes they have to fund them. The income taxes and corporate taxes are mostly in line with Europe.