Now it makes sense - why Painter made active roster instead of Brandstater

Painter was ineligible for the practice squad. According to Phil B. Wilson, " A player with no more than five games on an active roster in a season can be on the practice squad. But a player with no more than eight games active over more than one season also can be on practice squad." Because Painter was the 2nd QB after Sorgi got hurt last year, he was active for the last eight games and is therefore ineligible for the practice squad. Brandstater was the Broncos #3 QB last year and was inactive enough to remain eligible for a practice squad.

So making Brandstater the #2 QB would have required either cutting Painter and finding another #3 QB to put on the practice squad,  or else committing a third roster spot to the QB position. By keeping Painter at #2, they can keep both of these guys around and have a real competition between them next year after Brandstater has had a year to learn the Colts' system. And if they need one of these guys to actually play a meaningful game (God forbid!), they are only stuck with Painter to finish the game when Manning goes down. They would surely activate Brandstater for the following game and could decide at that time whether he or Painter would start.