Most fans don't really "invest" in the team. Maybe they invest emotionally, but that's about it. Yes, fans buy tickets, they buy merchandise, etc. But that isn't investment, that's simply purchasing goods and services. If the fans actually want to invest in the team, then send your money in without expecting anything in return except for a small stake in the team.
It's a good point Oz... I guess I view the fan involvement as an ongoing investment: merchandise, games, my Center Ice subscription. Not to much the possibility of the new stadium being partially subsidized by the city. I know the last point is really what this is all about, but still, the fans do invest in the team just as much as the sponsors.
The sponsors don't invest in the either and they really have no ownership over anything. They pay money, in return they get advertising.
The owners are the ones that actually paid to purchase the team. They need to run their business (i.e. the team) to make money hopefully, otherwise, that team may not last forever (Atlanta). This sponsorship deal actually helps the fans be able to watch their team play. Without such sponsorship deals, the ability for teams to operate would deteriorate.