But look how they advertised the game. You only see the NCR Ranger Veterans everywhere you look. I didnt even know what the Legion or Mr House looked like untill I played the game (I didnt have internet at the time).
Because that's a wise marketing decision, nothing more.
Caesar's Legion, Mr. House etc are all new to the world of Fallout. The NCR existed before and the old school Fallout players will recognize them. If they wear NCR gear to promote the game, it will influence those that were disappointed with FO3 that this game is going back to it's roots.
I'd say canon points towards Independent Vegas. Generally the canon ending is the "good" ending, and NCR and Independent are the only two endings where everyone and their mother is satisfied. With House, it implies Rose of Sharon Cassidy commits suicide (at least that's how I interpreted it), Veronica will be unhappy, Arcade will leave the Mojave, the Kings might die etc. But that's not why I'd say Mr. House isn't canon. I'd say Mr. House isn't canon because his ending is TOO good. He promises a path back to productivity, even space travel. Some people complained that New Vegas is too advanced and not post-apocalyptic enough. Well under Mr. House, Vegas would hardly qualify as post-apocalyptic. This game series needs conflict to survive, and under House there'd be no potential conflict remaining in Vegas. The NCR could fall apart and start a revolution if the devs wanted. Caesar could die and the Legion would fall apart. But if House lives, he's pretty much there for good. No one can take him out, at least in a believable way. I would argue that Mr. House's ending is almost TOO good. It wouldn't fit the "War never changes" theme. Independent Vegas though? You can give the NCR a bop on the nose, stop Caesar's Legion and let EVERYONE live to see another day, and still have plenty of room left for further conflict.