The use of "we" in sports

Why do people use "we" when talking about their sports teams?

For example, I often say, "we're playing the Dodgers tonight." While I know that I don't play or work for the Giants, I still feel a sense of ownership. Realistically, only fans of teams like Packers that are community owned should be entitled to use "we".

I'm unsure whether this is brilliant marketing or whether this is something inherent to sports. It can't be a coincidence that fans refer to themselves as nations.

Some die hard fans go as far as equating a team's wins and losses with personal success and failure. Silver Lining's Playbook does a great job of portraying the father's intense loyalty to the Eagles. While I've never been that emotionally involved with sports, I see the appeal in being part of the camaraderie between fans.