I'm guessing the only reason for various random scenes (or episodes) looking kinda crappy, is if CBS wasn't able to find some of the original film masters in decent condition and/or they were not willing to pay for an extensive restoration on the problematic scenes/episodes (back in 2001-2002)...
Is there any truth to the notion that the transfers were inconsistent on the dvd season sets after season 6 or so? (From googling and reading reviews on amazon and other message boards)
I wasn't really into the later seasons of Cheers. So I only picked up the seasons 1-6 dvd set when I saw it...