The reason most of us didn't notice was because this wasn't so apparent back then... the Alliance only had one mail-wearing class and the Horde only had one plate-wearing class. With Shamans and Paladins no longer restricted to one faction and with the introduction of Death Knights in Wrath of the Lich King, more classes appear to share the same item models -- there are three plate and two mail classes on both factions now. This has the downside of homogenizing appearance across classes but the upside of having the near-certainty of putting together a visually cohesive set as well as looking different from the enemy faction's counterparts.
So today's question is simple: what design philosophy do you think works best for World of Warcraft? Every path has its obvious benefits, of course. What appears to be the most appealing is something we still haven't seen... faction- and class-specific gear where each class has a completely unique model according to faction. It sounds great on paper but it's more work for the art team and an itemization nightmare -- imagine having to organize those drops in a dungeon! It might be easier to go the Sunwell Plateau route and be done with it! Or heck, do everything Emperor's New Clothes-style, where everyone goes commando! Good idea? No? So, uh, that was just me? Drat.