I'm with roy and wdlee. The difference is KG (and to a lesser extent Sheed).
Remember Orlando didn't even have Nelson for the Boston series. I think Nelson, Carter, and Barnes are better then Turkey, Alston, and Alexander and are just a better fit for that team.
KG is absolutely shutting down Lewis. He isn't doing anything. And with Sheed coming in off the bench, the Celtics can continue the man up defense on Howard that they just couldn't do as well last year when Davis, Powe, etc. were backing up Perkins and playing a lot more minutes at PF.