D&D1e vs. D&D3.5
I've known several role-players and Game Masters over the years who were reluctant or refused to update their games to the latest editions of "Dungeons and Dragons" (or Hero/Champions, RoleMaster/MERP, Storyteller, GURPS, etc.).
One reason is that if you've made the investment of money in rulebooks and spent the time to learn what's in them, why throw that away every five or 10 years? It takes a while for most player groups to make the transition, assuming they're even willing. I understand that publishers need to stay in business, but some updating seems arbitrary rather than for the sake of efficiency.
Another reason is that each iteration of the game has its own personality. I miss the Erol Otus art from AD&D1 and the Larry Elmore and Clyde Caldwell art of AD&D2. Different campaign settings rise and fall in terms of support in each edition--Mystara, Lankhmar, Al-Quadim, or Spelljammer, for example. Even with the boom of third-party D20/OGL publishers, few have captured the swashbuckling mystery and, yes, Monty Haul hack-and-slash roll-playing feel of the older editions. I think that's part of the appeal of games such as "Hackmaster" or "Castles and Crusades."
While I generally prefer to play the latest version of a particular RPG, I certainly understand the appeal of those who stick with older editions, although I think we should all be open to both the charm of the old and the (ideally) smoother game play of the new...