It wasn't banned, MS just doesn't want the crap they'll take from these anti videogame groups if they air it. They do show it at movie theatres though.
I think these commercials do the job of getting the point across about XBL to casual and non-gamers. You get the message of, hey, everybodys having fun, jump in. The image of a nerd sitting in a dark room, playing by himself, is not the image they want to project.
As for the people that want to see actual game footage... The ads are not geared towards you, they're for a different audience. They do have commercials with game footage, but they also get the main theme across.