I consider it "easy" in that it's accessible to the solo player. There is content there for guilds that want a challenge and to be at the cutting edge. But in "pre-WOW" Everquest, for example, just getting to the maximum level required a group of players. I'm not talking about farming gear or killing boss mobs or raiding. I mean just to get experience for your levels. Questing was horribly implemented and there were no instanced dungeons, so most of the time you had to grind mobs. And even mobs that were a few levels below you could pound you into the ground, save for a few classes that could solo with varying degrees of effectiveness. Experience gain was horribly slow, and if you died you lost a large chunk of experience (and you could lose a level, as well). When you died you rezzed automatically and were at your bind spot with none of your gear, which was on your corpse, which you had to locate and loot. And so on and so on.

When WOW came out, you could solo to 60. You can solo to 80 now as well. Gear progression via quests is decent (in "old" EQ you could go 40 levels or more before getting your hands on an item with stats). Instances and raid zones require groups, and the harder content requires a minimum level of competence, but getting to 80 can be done alone, and gearing up for heroics and raids allows you to progress in manageable steps. Don't get me started on raiding in EQ. *shiver*

That's what I mean whenever I say that I feel that WoW is easy. It's simply more accessible to the casual and solo player, and more accessible to the small guild that groups or raids semi-regularly.