I think people are missing the main component to this thread.
Its not that game thats addicting, its socializing with people on the game which makes it addicting. When i'm playing by myself (doing dailies, leveling alts, grinding rep etr), its really not that i'm having that much fun, its that there is some reward at the end of the hard work which i'm looking forward to. On the other hand, when there is a group of my friends hanging out in mumble, I feel like I could play the game for days while having fun, and not really want to do anything else. The social aspect of MMO's is what makes them addicting, and its human nature to crave communicating and playing with others.
That's pretty much the whole concept of WoW. You have to do stuff you don't really like in order to be able to do the stuff you do like, or get the things you want. Dailies are the perfect example. If you want reputation and some nice rewards, you have to grind dailies every day to a point where it just becomes really annoying. At a moment like that, I lose all interest in that part of the game and if raiding doesn't satifsy my needs, then there really isn't much reason to play anymore.
WoW is about setting goals. You want that PVP weapon, so you do a lot of PVP. You want that mount from exalted with a faction, so you grind dailies. You want a second char to do LFR before reset, so you farm dungeons (to reach the ilvl requirement). Everything in WoW = make your way through hundreds of meters of crap filled pipes before you are free (movie reference!).
I have taken yet another break from WoW. Unfortunately, I will probably come back. Right now, I'm thinking: QUIT! But in a few weeks/months, I'll be thinking: YOU CAN PLAY ANOTHER HOUR! That's the addiction part. WoW still offers something other games do not. Pretty sure it's that you get to do everything all over again every week; you're never done, there's always something to do.