One possible answer is that the Broncos think a quarterback-needy team out there will claim him off the waiver wire. And if a team does that, they also pick up the rest of his $7.4 million salary.
The timing of this is curious because in the last week several teams have had injuries to their quarterback. There's Matt Cassel with the Chiefs, but Orton doesn't make much sense in KC because they're not really in the postseason race.
But two more teams that suffered quarterback injuries -- Houston Texans and Chicago Bears -- make a lot more sense for Orton. The Texans have Matt Leinart working behind Matt Schaub, who suffered a potential season-ending injury last week. The Bears, of course, are Orton's former team and they're dealing with Jay Cutler's injury, which could sideline him for the rest of the regular season. In Cutler's place, the inexperienced Caleb Hanie steps in.
The question is whether Orton makes their team better in the short-term. We haven't seen Leinart nor Hanie work in extensive action yet so we don't truly know the answer to that question but there's an argument Orton can immediately make both teams better.
Keep an eye on the waiver wire this week. It'll be interesting to see if anyone decides to pick Orton up.