Since 1980 everybody's tax rates have gone down about half. However, since 1980 the top 1%'s after-tax income (real, adjusted for inflation) has gone up about 155% while the income gains (after tax) for the middle 60% are about 37% over that period.
http://www.cbpp.org/cms/index.cfm?fa=view&id=3629
U.S. Income Distribution and Mobility: Trends and International Comparisons
http://www.fas.org/sgp/crs/misc/R42400.pdf
"Another indicator of the degree of inequality is the Gini coefficient. It is a single number that can
range between zero (a perfectly equal distribution) and one (a perfectly unequal distribution).9
The historical trend in the United States is one of almost steadily increasing income inequality
(from 0.386 in 1968 to 0.477 in 2011), as depicted in Figure 1. During the 2007-2009 recession,
the Gini coefficient fell slightly from its previous peak in 2006 of 0.470. Its level since then
indicates an income distribution that is much more unequal than in most years since 1968."
In a comparison of Gini coefficients of 18 countries, the U.S. came in third from the botton (that is the third highest) with only Mexico and Columbia coming in worse than the U.S. Among the countries with better Gini Coefficients were most of the economically developed nations and Slovenia and Poland... and Greece.
GINI coefficient international comparison
__ also, income taxes are not the only taxes people pay to the government. Payroll taxes hit lower and middle income groups and when this is included the tax rate applied to all income groups comes out to being pretty much the same - that is, it is not progressive.