AI's contract is up after the season, so the Pistons will be able to clear some cap space. Also, Iverson will be open to a lesser deal and if he can still play effectively, could help the Pistons a lot.
Detroit always had a problem scoring a lot of points, having Iverson on the team helps address that! Billups had come up small in the past several playoffs, and this was probably the best opportunity that Dumars saw.