WoW isn't all that different from recent boom-bust cycles that we've seen in the economy, especially all the recent stuff with housing and risky mortgages.
Making something easy draws people in. It's an almost universal tactic to get people hooked. Banks give out loans like crazy with low interest rates. Credit card companies hand out credit cards like business cards at a trade convention. Leveling is no different.
Leveling is easy. Too easy. It can be done entirely alone with no knowledge of how to effectively play a class. Teamwork is not taught. I've heard of rogues that never learned that they could use two weapons and warriors that never learned defensive stance. The basic mechanics like aggro are completely misunderstood, and no, this isn't just because there is no built-in aggro meter; solo play just doesn't teach how to work in a group.
The result is a lot of people that do not know how to play effectively. But they had no serious problems while leveling, so from their perspective they are doing just fine. Is it any surprise that so many respond to advice with "don't tell me how to play!" even when offered in a helpful manner? Should we be surprised that raid content is left almost untouched by the vast majority of players? It's not that it's too hard or that getting 25 people is hard; it's that until they hit 70 players will never have any real barrier to advancement.
The easier it is to level a class, the worse they will end up. Take hunters for example. Ignore all the crap about noobs being attracted to the cute pets or pretending to be Legolas. Overall I doubt the average hunter is significantly stupider than the other classes, or at least not enough to account for impressions of them. The problem is that hunters are absurdly easy to level and offer little challenge to the player, so they never learn. It isn't that the player is stupid, it's that he's uneducated. Is it any wonder that hunters do poorly in high-end PvP when they never need to learn anything beyond auto-shot and mend pet? Buffing them won't fix anything.
Instead Blizzard should turn things around. Don't buff classes, nerf them. Weaken pet aggro early on so that hunters have to learn how to kite. Make proper use of traps needed to be able to complete the early pet taming quests.
Less specific to hunters, add challenges to be able to level. These should not be extremely difficult, or even really much of a challenge. That risks the loss of subscribers due to frustration with roadblocks. But make them test basic skills like knowing to save shocks for spell interrupts rather than just mindlessly spamming them, using stuns as interrupts rather than just more buttons to press, using fear in close areas, requiring the use of curse of recklessness to toggle it on and off.
Make NPCs give advice. This is something that is strangely absent in WoW: the NPC that tells you how to do the basic stuff. All the FPS I've played had some form of brief tutorial, a few minutes to get the player figuring out WTF he is doing. Next time my shaman talks to a troll I want to hear: "Ey, mon, did ya know dat if you drop earthbind totem and searin, you can run an enemy in circles and burn dem dead?"