DC – i.e., government employees – got richer compared to the rest of America. What also happened back then was a newly-Democrat Congress adding hundreds of billions to government spending, followed of course by President Obama and his 2009 “Porkulus”.
UPDATE (from Dan): Here’s something to chew on, Jeff, the difference between the governing class and Americans may be considerably greater than this graph suggests. Bear in mind the vast differences in income in the District itself with many blighted areas in the North- and Southeast quadrants of the city. And if incomes there would be pulling down the overall average, some folks living in Northwest (and the gentrified areas around Capitol Hill) would be earning far more than this graph suggests.