Excellent analysis so far, but I wanted to go ahead and throw in some of the issues I saw with the Bears:
1. Playcalling on offense. It seemed like the Bears stuck to the same game plan they had all year, even though they didn't need to. They would run the ball to get in short yardage situations on 2nd and 3rd downs, then drop back and try to hit a double-move for a big play. Unfortunately, it is virtually impossible to get behind the Colts' defense. the Colts' D is vulnerable to a team that can methodically run the ball and complete short passes to keep the chains moving. The Colts and Bears run the same defensive scheme, but apparently the Colts are the only ones who knew how to play against that scheme. The Bears kept going for those big plays, and it didn't pay off.
2. Rex Grossman is not very accurate. Those two interceptions were flat out bad throws by Rex. The one to Bob Sanders should have never been thrown because he has too much speed to get back across the field when you throw it up like that. The other one, though, should have been a TD for Chicago. The Bears receiver (I think it was Berrian, but I'm not sure) had the guy beat, and the safety had taken a bad angle. Grossman threw it about 10 yards shorter than he should have thrown it. If Grossman throws it up the field instead of to the sideline, it's a TD (14 point swing) and a totally different game.
3. Losing Benson shouldn't have been that big of a deal. I know Benson and Peterson (the 3rd string RB) have different running styles, but Thomas Jones' "slashing" style was very effective, so the most pressing concern was keeping him fresh. Peterson could have done that, because we have seen him have some very good games pulling backup duty over the past few years. I think the injury to Benson had little impact on the game when you consider #1 and #2 above.