Philly's interior defense is more vulnerable (slow, don't cover as much ground or provide as much shot blocking). Sixers have the better perimeter defense (more active bodies, gang defense).
I think Miami when they are at their best defensively are better than Philly at their best.
The Sixers were the more consistent team defensively this season but with this being the playoffs and all ... I'd expect Miami to give a much greater and more focused effort than they did in the lockout jam-packed regular season.
As for Boston, I think their offense matches up a bit better against Miami's defense than it did against Philly's.
I'd say the main difference is with Rondo. He doesn't have to go up against Evan Turner and Jrue Holiday in this series. I don't know, maybe they'll put Wade on Rondo instead of Chalmers and maybe Wade can do a job but he hasn't been great on Rondo in the past. Better than Chalmers but not as effective as Turner was.
I also think Ray can get more joy against Wade (cheats too much) and Chalmers (doesn't defend SGs well) than he did against Jrue Holiday. Well, if he is healthy enough to do so. But the opportunity is there if he's healthy.
I'd also say Bass could get a bit more inside against those small-ball lineups than he did against Philly's length (Brand/Hawes) in the paint.