Well, Sirius may have just pirated the home town broadcast. As far as I know, the Vikings games are broadcast on KFAN, which in an ESPN radio station. I don't think Sirius can use ESPN material, though I'm not completely sure of that. The Bears games are broadcast on 780 AM, the local news radio station, oddly enough. I think 780 is owned by CBS, and therefore might be able to sell their broadcast to Sirius. I admit I'm guessing on a lot of the legal arangement mentioned in this post, but it's at least a theory as to why you heard a Chicago biased broadcast.
I heard a commercial for NFL on demand. It shows the highlights of the all the games from Sunday. So far it is free. I think its only for digital cable though, which I am lucky to have.
I checked it out when I was home. It had about 13 minutes of every game and showed the key plays and the scoring. Not bad. When you watch the Viking/Bears game, they definately had Bears announcers. I never heard such bias and unprofesional announcing. Groaning and complaining. Im certainly not used to that, growing up in the NY area, not being a fan of those teams. Now living also near to Philly I hear it a little with there broad casts, but not as bad as that game. The credit said the radio announcing was done by Sirius.