Unfortunately that, right there, is the key.
No, this game doesn't mean much to the Colts, but under any other circumstance I would still think Indy would play to win. However, things are different since, if Denver and NY both win, Indy will play Denver again the following week in the playoffs.
Now, if you were Dungy, would you rather play the pathetic Broncos, or the red-hot Bills, in the playoffs?
If the answer is the Broncos, then the right move is to play very vanilla and let Denver win. The Jets, in all likelihood, will win as well, which means you then get to play Denver at home in the first round.
Even if the Jets lose and the Bills win, that just means they get to play the Bills, which is unfortunate for them, but at least they tried.