In fairness to Bruce, they started that campaign a couple of seasons ago about him supposedly being such a dirty player, and the league played along. They sent a message through the zebras, and that was when the sudden "change" in his game occurred. It's like when a guy is playing with 5 fouls - he has to back off a little, and that makes him a target.
I'll finally go on record - that is one of the 2 big incidents that made me hate Stu Jackson so badly. He put the word out to the refs to specifically start blowing more whistles on Bowen. Not just to call certain types of plays closer - but to specifically whistle Bruce. It's also the thing that finally made me completely turn on Steve Kerr, because that whiny was one of the major drivers of that campaign against Bowen. He not only called the league office down, he used his time with the Spurs to lend "credibility" to what he said.
I don't really know if Bruce has lost a step, or if he had to back off a step. I do know that he now draws whistles for things that other defenders regularly get by with. (Or worse... Derek Fisher's "belly-bump" defense comes to mind, but there are many others.) Whatever the cause, not having Bruce there to lock down one player may be the single biggest thing that separates this Spurs team from thos of the past several years.