The MMO blogosphere is full of people talking about Mists of Pandaria. Some, of course, lament the fact that the Blizzard fanboys are going back to WOW even though there are newer, better offerings out there like Rift or GW2. Some laugh in glee at all the haters and quitters who can never get fully over their WOW addiction and who always come back for just one more hit, and some welcome everyone back to the fold.
There are all kinds of theories about why exactly this happens like 'WOW is a security blanket' to 'Blizzard makes the most polished product out there' and those probably have some merit but they aren't the answer. The real reason people end up back in WOW is community. It is the same reason that D3 fell flat in my group of friends - grouping was substandard in terms of progression and communication was clunky. The game itself was good enough to keep us playing a long time but the community wasn't. When I used my free week in WOW and logged back in I found tons of my friends doing the same thing, getting ready for Mists by doing achievements, reading up on strategies for getting realm first professions, and testing out content we had missed in our time away. I saw people there that I remember from raiding but whom I have never seen outside of WOW too; it was a full house.
That full house was the key. I love having an online community, especially one I can access any time. Sometimes I want people to talk to during the day and being able to log in to a game and chat with friends is a wonderful thing. WOW has the huge advantage that everybody has played it, so all kinds of people reconnect when expansions hit, and also that it has a massive subscriber base normally so I probably know all kinds of people who are slaying monsters and taking stuff.
The gameplay in WOW is good, don't get me wrong, but the gameplay isn't the thing. People will do almost anything for friendship and love, including playing awful old games like EverQuest. (If you don't buy that, just ask a EQ veteran to tell a story that doesn't revolve around either "Boy, was EQ bad" or "I had lots of friends in EQ") Once you develop those connections with people you want them back and WOW is the biggest hub of connections there is for hardcore gamers. In this way WOW is like Facebook; even if it isn't the best it is the biggest and in a social network being big is even more important than being good. I am on Facebook even though I think its design stinks and it has all kinds of terrible ethical lapses simply because the connectivity it offers is too useful to ignore. WOW is the same way; I want to see my friends and they are playing WOW so WOW I must play. Not that WOW's design irritates me the way Facebook's does; WOW isn't perfect but it isn't terrible either.