I guess all teams hold their preseason games at their own arenas for their local fans? The Cowboys don't have any obligation to host their preseason games at the Alamodome if they have camp there. They probably wouldn't even sell 1/3 of the seats for a preseason game...no one gives a about preseason, and the ones that do probably just want to watch some football, so they'll watch it on TV not go to the game. Seriously if someone handed me tickets on the 50 yard line with paid air travel and hotel to Colts preseason games I wouldn't even go.