At first I thought 'biggest selling' not fastest selling, and I for the life of me couldn't work out how and expansion could outsell the original game.
While I'm no fan of the paid for services like name changes, class changes, pets, mounts etc, so long as they never stray into giving people actual in game advantages for cash, I'm fine with them giving people an option.
If you've not played both original WOW and Cataclysm WOW , then you just have no idea how wrong you are to say they've just dumped some lava on a few maps and charged people another $30. I was looking forward to Cataclysm as I enjoy the levelling more than the endgame, and I've been so pleasantly surprised by how much they've packed into this, so much more content than I expected.
I expected a lot of the Azeroth zones to be shaken up and look different, sure, I didn't expect them to pretty much throw the whole original game in the trash and rewrite nearly every zone with new quests, npcs, etc.
On top of that, after 6 years, they're still making big changes to balancing the game and making it more user friendly.
This isn't a case of Simon Cowell backed karaoke singer gets to number 1 cos he's well funded and popular, but lacking in talent, its more a case of someone pouring money into a talented band so they can be the best they can be.
Popular fads fade, people wouldn't still be with wow years down the line if it sucked.
Of course, you're welcome to hate WOW, whether you've tried it or not (and damn, the limits on the demo are stupid and its no wonder so many people quit after trying it), but, I like it and I consider the £10 a month a bargain compared to one PS3 game a month, which I'd hope would captivate me for four weeks solidly.