@ HDS-
Well, the World Devestators were also armed, so I imagine they destroyed other vessals as well. One example would be Silencer 7. I would imagine anything that can devoid a planet of life counts as having destroyed a planet, in addition to actually "blowing them up".
In addition to those things, you're also leaving out Alderaan (which we saw destroyed in New Hope) Theres also the Eclipse super star destroyer, it had a superlaser on it. See, with the Empire it wasn't about destroying planets, just terrorizing them by "setting an example" by "executing a planet" so they'd submit to imperial rule, those neutral or alliance systems which weren't already imperial. Its about conquest, not destruction. Afterall, you can't take over a system you've destroyed.
So I'm sure that in total the Empire destroyed far less than a 100 planets, but if given time could have destroyed 100, or even more, though it would have been unnecessary, and more systems would revolt because of it, and that just makes the New Republic stronger, and the Empire had lost it's grip on the galaxy by this point so it couldn't be everywhere at once to maintain law and order.
@ Ness- Yeah, I was about to tell him that. MOVIES. 😛