Once you make it to the endgame, yeah, it's very horribly addictive. I was doing raids thrice weekly and spending the other days grinding materials for it. Especially now, when you can level essentially any way you want. They brought in experience for PVP and professions, but there's a lot more PVE variety in WoW than in EVE. It just takes a lot more research, since techniques change from raid to raid and boss to boss. I'd say it's a lot less about correctly itemizing for playstyle and more about being able to fluidly react to changing environments. And if PVE is all about that, the PVP stuff puts raiders to shame.
It's almost like you finally get bored of something, but there's a completely different thing to do that just sucks you in. I did pet battling for 6 months. For a glorified Pokemon ripoff, it just drinks your life.
If you only got to 40 and stopped, leave it that way. If you ever develop a network of friends there and really get an instance group going, it's very hard to stop.