I've played wow for 2 years now.
Tried Guild wars went back to wow,
Really tried Star Trek: Online.. went back to wow
The thing that brought me back to wow was investment. I have a lot of time spent on one character (my highest alt is lvl 20) and as a result of that i can't/won't start another MMO because firstly i don't have the time, and secondly i don't have the patience to start something that big all over again.
When my account was hacked and everything stolen. i came within a hair's breath of quiting, because with the loss of all that investment the game simply wasn't appealing to me anymore. The strange thing was i was gutted, but filled with a small sense of relief in that i could just drop this game now. Un/Fortunately Blizz were able to fix everything within an hour so i went back to it.
I won't play any other MMO because im not going to do what i did with my main character again nomatterwhat, but also since Blizzard and wow has turned into this mammoth TiTan of a thing, i know the customer support will be excellent, the fan base although varied will always exist, and new content will always come out to make the game fresh.
The Gear reset thing i don't actually mind. I was a middling lvl 80 till ICC came along with its frost badges, i just collected them and now im a high ranking lvl 80. It made an awful lot of the game available to normal players and forced a lot of previously high geared players to drop the 'holier than thou' and bad attitude act because everyone needed each other again to explore and play the new content.
I know cataclysm is going to undo a lot of the time i spent in ICC and other instances but it won't undo the rep, the achievments and change the fact that i had a good laugh with the guild in these areas.
As for PVP, not my thing, but wow is big enough to ensure there is always something to do, bit it instance raiding, questing, mundane fishing grinding, or Arena's and such. No other emerging MMO will start off with all this available or polished...
As for the Star Wars MMO... i hope for the sake of all the Star Wars fans that its a success. I had very high hopes for Star Trek online, and to be fair i enjoyed some of it, but i just couldn't play two MMO's, i don't have the time, patience or energy and Wow won out because it was at that moment better and mainly because i already have so much time invested on one character in it.