I never say "us" or "we" when referring to a team I am not an actual member of, but that's just me. I do notice; however, that the players never say "we" or "us" when referring to fans but they simply refer to us as the fans. I do say "us" when referring to football fans. Even if I were a lifetime season ticket holder and had scads of Cowboy merchandise, I would not refer to the team as "us" because I'm not on the team nor employed by the team. They won't let me in the clubhouse and they call it a club for a reason - members only.
I don't have a problem with those who say "us", whatever gets you where you wanna go, I just don't feel I'm a part of the team, only an outside observer.