That's pretty misleading. The median net worth of a member of Congress is about $1 million: http://www.opensecrets.org/news/2014/01/millionaires-club-fo....

You also have to take into account that the average age of Congress is almost 60. I.e. they have been working and accumulating assets for decades. Adjusted for age, the net worth of the median Congressman is at the 80th percentile: http://www.census.gov/people/wealth/files/Wealth%20distribut.... Is 80th percentile "wealthy"? It's within one standard deviation of the median. I'd call that upper middle class.

Fun fact: the median doctor is worth over $1 million by age 50, and about $2 million by age 65: http://www.medicalpracticeinsider.com/news/which-doctors-sta....