Fantasy football. For real.
When I was in Arizona last fall, I went to a Scottsdale bar to watch the Packers-Vikings game. Every other table had at least one guy one a laptop. I talked to these guys at the table next to me (also Packer fans) and they were keeping track of how their fantasy teams (usually more than one) were doing. I suspect there may have been some financial reward for the winners in their leagues, though they did not say.
When I got back here, I talked to a friend of mine who is manager of one of the sports bars here in town. I didn't know they had wireless, but he told me hell yes they did, and he confirmed that sports bars all over the place are getting a wireless hookup for that very reason.
Finally, go here
to see what the guys at Football Outsiders say about what makes a great sports bar (I have a comment near the end- not about wireless). They don't specifically talk about the reason, but I think it's inherent in the discussion.