As time went on WoW became more complex in an effort to continually challenge its players. New game mechanics were introduced and corresponding stats showed up on items to deal with them. Classes took on new roles and new game mechanics were introduced to cater to it. Multiple sets of gear became necessary to deal with the many different encounters available in Azeroth and the Outlands.
But now, with Wrath, Blizzard is simplifying the game to a great extent. Item stats are being merged or removed (hello, +Spellpower.) Different classes are approaching encounters the same way (all tanks are getting better at AE abilities). Raid boss mechanics, which only a small percentage of the player population has seen, are being reused in more accessible encouters.
So the questions is: Do we want a more simplified WoW so we can spend more time playing and less time analyzing dps charts or is the complexity of the current game part of the appeal?