Want to live in one of the richest counties in the US? Move to Virginia or Maryland? What makes them so special?

If you want to live in the one of the Top Ten richest counties in America then you should move to a Washington D.C. suburb in Virginia or Maryland...Hmmm...I wonder why there is such a concentration of wealth in that area?  When political power and taxpayer money are vast and concentrated, the rent-seekers (lobbyists/corporations/other do-gooders for my welfare) will be vast and concentrated too...Only pointing out a symtom, not the illness...(via Newmarks Door)