I read the ads are aimed here too -- ads broadcast in the Twin Cities reach into western Wisconsin so they get a bit of a two-fer. Per:
http://minnesota.cbslocal.com/2012/10/28/talking-points-the-2012-election-will-be-a-toss-up/
In response to tightening polls, Romney did start running ads in the Twin Cities over the weekend but it was a small ad buy that was countered by a small number of ads run by the Obama campaign.
Thankfully these are small ad buys. I am so so sick of the Cravaack ads against Rick Nolan, and I only watch commercial TV on Saturday and Sunday just to catch the news (since there is no PBS Newshour on the weekends).