A couple of questions:
Why, if the Legion rules over at least some portions of the huge states of Utah, New Mexico and Arizona, hasn't the Legion tried to outflank the NCR in the Mojave altogether instead of funneling all its strength into the tiny bottleneck of the New Vegas vicinity, where the tech advantage and infrastructure of the NCR is most potent? The NCR is in a 'holding pattern', which explains why they haven't tried to do this to the Legion, but why hasn't the Legion done this? Seems to me like outflanking the Hoover Dam (say, assaulting New Vegas from the north) will stretch NCR resources and war exhaustion even further, and lower population concentrations is to the Legion's advantage, given their low-tech nature and their willingness to use psychological terror tactics (ala Nipton).
Of course, I think that question is somewhat dependant of this one: how big exactly are the NCR and the Legion? We've had vague clues so far - we know that the NCR is in Southern California (San Diego, Los Angeles, etc) and Baja, but how much exactly of (modern) California do they occupy? I'm not that familiar with Fallout lore (came to the series with FO3), so if anyone knows if there's a mention of the NCR's northern limits anywhere, do tell. Same goes with the Legion. An actual map would be even better.