Actually the exact opposite is happening. The top quintile is pay a bigger share of taxes than before.[1] In 1960, the top quintile paid 56.5% of all federal tax revenue. In 2005 it was 69%.
Care to revise your position based on that?
[1]http://www.nbcnews.com/id/29861648/ns/politics-capitol_hill/... (table on right)