[softwaredoug]

DC is a region of various "downtowns" connected by the metro / beltway. Tysons Corner, Bethesda, Silver Spring, Rosslyn, Alexandria, are all their own business centers with their own neighborhoods, themselves walkable. Each looks like a medium-sized US city downtown. Each has its own anchoring agencies / businesses that define the economy of the area.

[senkora]

This. DC does transit-oriented development, where the areas around metro stations are densely zoned, quite well.