Basically, I think this is a move of necessity on Romney/Ryan's part and one of caution on Obama's. With Ohio looking harder and harder for Romney, they need to look for some other path to get to 270 and Wisconsin is one of the more plausible ones out of very poor options. For Obama on the other hand, nailing down Wisconsin assures 270.
The current PollTracker Average gives Obama a 2.2 percentage point lead. The polling of this still fairly critical state has actually been kind of thin. Of the last 10 polls, four are partisan or advocacy group sponsored polls. Two of the remaining are internet polls. And two more are Rasmussen polls. The last premium live caller poll was NBC/Marist on the 17th which showed Obama +6, and just a few days before that Marquette Law School which showed Obama +1.
Basically, I don't buy the idea that Romney is somehow on the move in the state. But it would be nice to see a premium live caller/cell phone poll in the state. It's wrong to conclude that the Obama campaign thinks there's a problem because Obama is going to be in the state next week. But clearly it's a state that's close enough that they don't want to leave anything to chance.