There are several shows they won't re-air on regular TV for some reason. And even when they DO air the originals on cable they butcher the hell out of them to get more commercial time in there.
I read somewhere that Nick at Night was cutting off 3 minutes of the orignal episodes! That's a big chunk when you're only talking about a 24 or so minute show to begin with.
And they were BAD at it too. They would remove important scenes so that the characters would be talking about something and you didn't even know what they were talking about because the scene describing it was removed!!! GRRRRRR!