If it helps you, I'll rephrase. I'm fairly confident that people would have complained if any of the factions from the previous games not been included.
I wouldn't. Nor would many other fans of the original games. I wouldn't mind if a faction from FO1 or 2 made an appearance, but pretty much all the major players in the Capital Wasteland seem to be transplanted from the West Coast. The Brotherhood of Steel was originally a local, isolationistic faction that starting with Tactics suddenly became an organization whose various splinter factions encompass the entire United States.
Quoting Jesse Heinig, one of the makers of FO1:
I've played Fallout 3 and I enjoy it quite a bit. I think that Bethesda made a great game and they did an excellent job of paying homage to the Fallout continuity while bringing some fresh, new ideas to the table. I think that what I would like to see in a future Fallout is the same as addressing my only real issue with the game: All of the old familiar elements of the Fallout world migrated to the east coast, so we have the Enclave, the super mutants, the Brotherhood of Steel; I'd like to see more new groups, more power factions and societies that have sprung up in a big way. I get the feeling from Fo3 that there's a sort of "power vacuum" in the east and that these groups moved out there to fill that hole, but this is probably not the way things are going everywhere. I bet there are other big groups out and about making their mark on the wastelands, some of whom may have crossed swords with the existing power blocs, others who have never heard of 'em. (See Caesar's Legions in the design docs for Van Buren - a large, organized power group that runs the show in a particular area of territory.) I'm glad to see the BoS and the super mutants and the centaurs and whatnot, but I don't have to see all of the old groups to know that it's Fallout. I guess we don't have Followers of the Apocalypse in Fo3, though. Most of the new power groups in Fo3 are relatively local in the game, such as Rivet City (which is a thriving metropolis, but it does not try to project its power across the Capital Wasteland) or the Temple of the Union (which is an awesome idea but I get the sense that they're very "new" and not super influential). Anyway, for future Fallout games, I hope that Bethesda (and Interplay, on V13 - assuming it is in fact Fallout Online, 'cause I'm not in a position to confirm anything) continues to look at the franchise with a critical eye and say "How can we tell interesting stories in the same vein established previously for Fallout?" I'm really looking forward to the downloadable content. I really want to see the Pitt.