I think a lot of the "we" stuff stems from the fact that the person that is a fan of the team generally supports them by purchasing tickets, attending games, buying merchandise, etc, so they feel like they are apart of it. Yes it is the owner that signs the players' checks, but it is the fans that gladly hand the owner the money to do it.

Then you can just go to "us vs. them." Yankees/Phillies World Series from a couple years ago. New York beat Philly. Modern day war between city/states for bragging rights. Instead of NYC sending 10K troops to burn Philly to the ground, they send 25 guys w/ bats and gloves to take their pride. Instead of looting treasures, the winner gets a ring. Instead of raping their women, the players fuck their strippers.