WoW (and the popularization of MMO's in general) has changed the way gamers work, and the general public will never be able to fully accept a random loot game anymore. They need to know that when they kill X mob... W, Y, or Z item can drop but you know going in that they are upgrades for someone you are playing with. No one wants to deal with vendor fodder anymore or the off chance that a good deal of effort may result in a random item that no one can use.
Poor itemization in BL2 will be the first thing (Well, one of the first things... I'm sure...) everyone starts complaining about. 87 bazillion weapons and 12 good ones, just like the first game.