OD&D - The perfect dungeon based roleplaying game, with dungeons. Just where the hell can I buy Chainmail?!
BD&D - Pandering to the Rogue-like crowd. Also, when my DM's in a bad mood with me and make up biased rules.
AD&D - Pandering to the Dungeon Master crowd. Also, can we not start at 5th level and I play a Wizard? With psionics?
2D&D - Pandering to Diablo crowd. Also, whoo, this all tastes a little Vanilla.
3D&D - Pandering to the Ultima Online crowd. Also, while I've spent 40 hours perfecting my NPC liche, it's too complicated to actually run.
4D&D - Pandering to the WOW crowd. Also, it's only fun when actually, you know, playing the game.
Now T&T, there is a game.