Baltimore and Washington are essentially the same metropolitan area these days. Years ago, most cities that had big league teams had two, one in each league, but those days are long gone. Only New York, Chicago, and LA/Anaheim seem able to support two teams these days, plus the Bay Area -- which, as noted above, has had its problems. Without that really beautiful new stadium for the Giants (my once-beloved Jints), they and the A's would probably be hurting.

At least the AL Orioles and the tranplanted NL Expos would represent the two leagues.

As I understand it, there are two competing groups, one in DC proper and one in Northern Virginia, bidding for the Expos. Seems to me that the Virginia suburbs might stand a better chance of surviving in the same market with the Orioles, just because their stadium would be a little further away from Baltimore than one within the district.