Addiction comes from strict but appropriate rules, objectives and rewards, it is absolutely nothing to do with graphics or the setting.
The social aspect is also a huge part of it. The fact that it's a "persistent world" means that if you're not on there gaining experience means someone else is.. essentially you're not using all the potential given to you. It's even worse if you play with IRL friends as it'll be all you talk about and of course you end up extreme competition with them levels wise.
I've never found that my RL group of friends who play are competitive at all. We wait on each other to do group quests or instances, we level together and just generally help each other out. For us it's just a way to waste some spare time and have fun.