I am playing WoW right now - in fact I got to 50 with one char and I have two other chars, one at 42 and one at 37, and many lower level ones. I don't know if it's something wrong with WoW, or it's because this is Beta, but I don't see the reputation difference between Diablo 2 and WoW that you speak of. We are not talking here about going from D2 to a MMORPG, but rather from D2 to WoW, so lets stay on track. The difference? I know that certain games (SWG for one afaik) have even the gameplay revolving around the actions of the player (and thus in part his reputation). But I have seen little in the way of reputation affecting anything in WoW.
A lot of your gear can come from quests/drops/trading. You can EASILY just solo the entire game, at least if you are alliance. As for the instances and their wonderful drops, if you are a warrior or a priest, you WILL get asked to do some instance runs, even if you messed up several times before. If you are a Warlock, you probably will not, no matter how good you are. Reputation just doesn't "hugely" matter much right now, it has almost no influence on your leveling and gear finding. I don't see how you can make a comparison of D2 to WoW if you haven't actually played WoW.
A lot of your gear can come from quests/drops/trading. You can EASILY just solo the entire game, at least if you are alliance. As for the instances and their wonderful drops, if you are a warrior or a priest, you WILL get asked to do some instance runs, even if you messed up several times before. If you are a Warlock, you probably will not, no matter how good you are. Reputation just doesn't "hugely" matter much right now, it has almost no influence on your leveling and gear finding. I don't see how you can make a comparison of D2 to WoW if you haven't actually played WoW.