Here's the thing that some people missed. The set up Avon put on Stringer wasn't out of revenge for D'Angelo, but his rep. (Of course D'Angelo getting killed probably made his decision a little easier.) Remember Brother Mouzone told Avon that the reason he's giving him a chance to give up Stringer was because of his word and reputation. He implied that if he didn't act as the stand up gangster, he was going to go back to New York and tell EVERYONE that he was not honorable. That would mean that NO ONE would deal with him in the future, and it's a possible "green light" on The Barksdales. Even though at that point Avon, and Stringer were getting the best product from Prop Joe & The Co-op (courtesy of Spiros and The Greek) there is no telling how bad it would have got for The Barkdales, and that is IF Avon would have gotten out of being kidnapped and tortured by Omar and Brother Mouzone first. (Omar confirms that was the plan to Stringer Bell before he was killed if Avon refused to give up Stringer.) Here are the recaps:
Avon and Brother