Why for Boston:
Boston is a "roles" offense. The players on this team play a role - and they always will, as long as Rondo is running the show. Rondo plays a role: he passes the ball; because he doesn't shoot, those he passes the ball to, ought to look for a shot. You can see this when you watch the games without him. The ball moves around a lot more. But, it's not as efficient. Over time, I think the Cs are better with Rondo facilitating, since the defense can't just clamp down on the "hot hand."
While it's true the Celtics are having a lot of defensive problems, much of that has to do with the WAY in which we score. We do not draw that many fouls (except for Pierce). If we could produce more big man fouls, it would give OUR big men (mostly KG) the ability to help off the inferior backup. If KG can help, then the guards can cheat: go for steals, force the guy to the off hand.
Moreover, Jefferson plays a role: he catches the ball in the post, and goes up with it. That's a good player to have on a team where everyone plays a role. He's a half court player, and we're (unfortunately) a half court team. With ball in hand, he draws a double.
A line up of KG, Jefferson, Pierce, Bradley and Rondo is weak defensively at the least relevant spot, in our conference. Who does Jefferson guard on Miami? Joel Anthony? How about on the Nets? Kristen Humphries? Tyson Chandler isn't throwing down for 25 points. I'm not worried about Taj Gibson; and I'm not worried about Andrew Bynum.
DeMare Carroll is, by most accounts, a solid defender who could spell Pierce off the bench. Taking Green's place, to some extent.