I've heard this one before and I've even subscribed to it for awhile. But I'm thinking it's rubbish now.
For the simple fact that WOW (world of warcraft) 'out-wowed' other mmorpgs. It took components from all of them and 'out-wowed' or more technically apt 'out-mmorpg-ed' them.
But even there I don't think its subscription numbers are due to 'out-mmorpg-ing' other prior mmorpgs.
It just had a wicked hot advertising campaign! An advertising campaign that quite possibly started well before the idea of seriously making a mmorpg even occured to anyone at blizzard.
The warcraft RTS games - it's all advertising for wow. Years in advance. Every single session of play, millions of them - promoting that warcraft brand.
Then every single other company goes 'HAI I WANTS MONEY LIKE THAT 2!' and makes a mmorpg. They even make, arguably, better games/mmorpgs than wow. But they don't do as well.
They just lack years of indoctrination...sorry, I mean propaganda...sorry, I mean advertising!
The guys who made torchlight, they put it out as a single player, with plans for some sort of big multiplayer in future years...they've got the idea!
Literally years of advertising before the product even exists. Advertising that people paid to aquire - an advertising campaign that profited in itself, let alone in terms of the eventual product sales/subscriptions. Think about it.