There are obviously a lot of factors in sub numbers, but when you look at the subscription graph, its kind of shocking how it just flatlines as soon as wotlk hits after ridiculous growth prior to that. It was not a slow, gradual run off where many things slowly ate away at it. It was a very sharp, sudden halt to the growth. And to me the single biggest difference between wotlk and BC game design was that in
many aspects, not just raiding, the game catered much more to casuals, which is why I attribute the decline to that.