Interesting point. You look at a guy like Amare Stoudemire and you wonder what kind of defensive monster he would've been if he'd spent his first several seasons in the league under a coach like McMillan. At this point, though, Amare is who he is, a decent shot blocker but overall somebody who just doesn't try hard most of the time on that end of the court.
Myself, I don't think transitioning to a faster-paced game was part of some sort of master plan. It just seems to me that time after time Aldridge was beating his defender down court and so he was being "guarded" by some 6'2 guy. You show any coach that opportunity repeatedly and eventually he's bound to think to himself, "If we just get the ball down there quickly, those are easy points."
Added to that is that Batum is so much better at running in a fast break than Webster or Outlaw. He's got a vastly superior handle, and he can make the quick outlet pass to a breaking point guard without the guard having to break stride. And he's just more competent at finishing--how often does he blow a dunk? How often does Outlaw?
Most teams see the move to upping the tempo based on either the coach or the guards. The funny thing about this team is that it seems to be our forwards who are driving it more than anything else.