What I think is Bethesda's biggest mistake in regards to Fallout 3 is that they haven't looked properly at where the Fallout fan base is. I don't mean what system they're gaming on, but in what part of the world they're living in.
Sure, the Americans are a large part of the fan base, but Europe, as a whole, looks to be at least at large, if not larger. Germany has released several well-received post-apoc RPG's. Russia is also releasing post-apoc RPG's, and it looks to me like Poland has the largest Fallout fan base outside of the US.
If Bethesda (and a big IF that is, since we don't know squat about the game at this point) keep the developing focus on the X-Box market rather than the PC market, then it seems to me that they're taking Interplay's old slogan "By Gamers, for Gamers", and turning it into "By Americans, for Americans", because I don't see the X-Box 360 having as big a market in Europe as it does in the US.