All those lists always have the three counties surrounding DC, why? Well, at the SOG is where you find all those federal bureaucrats who make 150K per year. They treat those in the outlands who work for the G like red headed step children. The farther out in concentric circles you go from that hole, DC, the lower the pay gets from my experience. The best thing for the country would be if the place were shut down.
There is really something wrong when the richest counties are next to our center of government and not our centers of business.