I think most of us appreciate what Manning has done (although I admit I do think we should've gotten more than one SB out of him but that's more of a management issue than a Manning issue with me) however we also do remember what the Colts were like before(a lot of us anyways) and we don't want to revisit it anytime soon either.
Look at the Dolphins and Broncos who have waited forever to get that next great QB after Marino and Elway and that QB never came(and they are still waiting)
We don't want the Colts to end up like that and without a great QB and a small market such as this we're on our way to being irrelevant.
It would suck if the last memory of Manning as a Colt was him looking at Caldwell in disgust for calling a bad timeout but unfortunately not everyone gets the Elway sendoff.
When it ends it just ends...