I agree. The article was pretty weak. The article talks about reward systems (items, XP bar, etc.) but that's not what makes games like WoW more addictive than every other RPG that has the same reward system. Some would say polish, which WoW most certainly does have, but that's not reason enough to be disproportionally committed to a game. Many Slashdotters have pointed out the community aspect of WoW as being a main contributor to its addictiveness, which is true, but there's one other important factor about addictiveness that I'm surprised I haven't seen discussed in articles about the topic, probably because they don't understand the psychology behind things like this.
The reason why WoW is so addictive is because the gameplay changes the more you play it.
At Level 1 there's tons of new areas to explore, leveling happens quickly, new abilities are different and exciting, and you are safe from the Alliance (I played Horde). Playing with friends was fun and informal. The game was casual and I could play whenever I wanted to because I could complete quests on my own.
Then we gained enough levels were we had to go into the contested regions of the game to continue playing, which meant that we were getting ganked by the Alliance constantly. We banded together into slightly larger groups for safety, leveling took longer, we hated the Alliance so we would go out of our way to kill them when the opportunity would permit, and the game slowly became less about adventuring and more about PvP and survival.
To continue leveling up you were expected to join a guild so you can go on regular raids, if one of your friends didn't make you join a guild already. Leveling took even longer, good items were harder to find because you had to share between 15+ people, the best items are dropped on raids so that's more incentive to run them, and people are now depending on you to be present at the raids, so you now have a schedule to keep.
So a game that started out as a relatively casual game that I've seen people get their non-gamer wives and girlfriends to play, slowly turns into a commitment. You can't just log in and play whenever you want, you have to be ready to run Molten Core every Tuesday and Thursday at 7pm, and that commitment develops so subtly you don't know what's going on unless you know what to look for, which is why I stopped playing after a few months. The incentives to play the game, and therefore your commitment to it, slowly changes in the same way the chances of winning penny slots changes the more you play it. WoW was designed so that the first 10 levels has such a wide reward system that most types of people can get into it, regardless of their reasons for playing games. As you level up the incentive and reward system becomes more narrow and more concentrated until the players become the type of gamer that Blizzardâ"or indeed any other game companyâ"wants you to be: a committed paying gamer, and for all the statistically right reasons.