This is pure opinion/speculation, but I believe any DC area school has more of a potential to be "National" in terms of placement down the road than other lower Tier-1's and 2's. I'm not suggesting that national firms might recruit directly, but if you wanted to move elsewhere down the road, time spent in DC can be leveraged in some valuable ways. If you can pick up any expertise dealing with Federal agencies, legislature, etc. you can take that to another state and market that to firms who what to offer that attribute to their clients but are unable to find it from regional schools in their area.
As far as GMU's rise in the rankings, I think they're the case study for why rankings aren't the end all be all. How many slots have they moved simply by giving away free online applications to the school to lower their admission rate to Ivy league levels (lower in some cases)? Don't get me wrong, the rules of the game are spelled out clearly for everyone . However, it's one thing to raise your ranking by raising your admission standards and still managing to fill a full class. It's another to flat out grossly exagerate one of the metrics just to obtain a higher rank. Their free online admission vouchers do come at a cost: How many candidates that might have qualities outside of their index scores really get properly evaluated considering the sheer mass of applications? Their way of handling admission further weights GPA/LSAT index scores and devalues aspects of the application that take time and individuals to assign a value to.