I've heard this analysis a couple times in the last 24 hours, and it sounds plausible to me. From First Read:
Meanwhile, in Indiana, don't underestimate the Chicago media market effect in the negative for Obama. Why? Local Chicago TV has been as obsessive -- if not more -- than the national media. No national media outlet, for instance, has asked their news helicopter to hover over Rev. Wright's house. How many Northwest Indiana households saw THAT?
Prior to last week, one of the reasons we all thought Obama would do reasonably well in Indiana was that the Northwest part of the state is basically in the Chicago media market. Now that's not looking like such a boon for Obama. It's hard to see how he wins the state without a strong showing there.