Well, the numbers I believe come directly from the IRS and from the 2006 year, if you take the time to compute the ranges, you can see that about 10% of tax payers either didn't pay taxes or received some money back.
I really have no idea where the huge numbers that you used came from, although in fact I have seen some websites claiming that 50% of Americans don't pay any taxes (those outrageous claims are erroneous).
When using the authoritative source for this particular statistic, progressive taxes don't seen so bad in the US.