Originally Posted by
melodramocracy
People tend to make personal judgement calls on sub losses, and given the half-assed nature of Blizzards exit survey, they probably don't have the best data they could either. Some will claim that Cata started the big decline specifically because of difficult dungeons. Others will say that it's simply because the game is old. If / when WoD drops subs further, rest assured that people will say it's because of the no-fly thing.
Universally? I'd say an MMO that is generally considered easy, or at least straightforward to finish at a level your average player finds acceptable, is one that is bound to not retain players for a significant amount of time. And the key here really is 'the average player'.
This is actually one of the larger problems that this game has right now, and the relatively high number of alts that people have is a very good sign that you have a number of subscribers who thoroughly enjoy this game, but there simply isn't enough for them to do, because so much of the content is quick to consume. For your fringe type of player, the one who needs every achievement, and to beat every aspect the game has to offer, I'd say it's a different story, but that's a small minority.
Then there are retention factors that have very little to do with the sheer difficulty of the game, such as the in-game community itself and the concept of you being represented by your character, but that's a different topic.