Read this:
http://www.politifact.com/truth-o-meter/article/2011/sep/21/does-secretary-pay-higher-taxes-millionaire/
Most super rich people find ways to shelter their money from being taxed. Investors and people who make most of their money through capital gains, or investing for others, can lower their tax burden to an unbelievably low level by classifying this income as Carried Interest. Some people may try and defend this, but I'm not sure why we have super rich people in this country who hoard money and have a lower tax bracket than the majority of people who make less than them, without needing the use of deductions.
Eric Schoenberg and Warren buffet, who both save tremendous amounts of money due to this rule, both believe it shouldn't exist, and their tax rates (and others whose income is classified as Carried Interest) should be much, much higher.