Let's test your definiton. What about Stormreach? It doesn't have a huge world, right? What is Guild Wars with your definition? A MUD? Not to mention that a lot of mmorpgs have servers that won't fit into your category, since they are run by fans, can have anything from 2 to 10 000 players and can be free to use.
Of course, you don't base any of your discussion(ergo arguments) to logic, so this is kinda pointless.