not all mmos require you to pay, but most of them require you to pay something. someone earlier mentioned maplestory as being free. what they dont charge upfront they charge in other ways. in most free mmos like maplestory they let you get healing potions that heal 50 hp and make you buy the healing potions that heal 5000 hp for real money. or they sell items that give you an experience boost of 10000% for an hour.
anyone who plays those games regularly has to buy these things if they want to play the game for any extended amount of time and not kill the same thing for a month. guild wars didnt use their own servers to run the game very much, the same as diablo 2. you host a game and others join it. their server cost is way less than other mmos.
essentially what youre paying for are the developers time to create updates to the game, making more content for the users to play through. DCUO is the same and SoE isnt new to this, theyve had houndreds of thousands (probably in the millions) of people (using very similar payment plans) playing their online games for over ten years. people pay for it because its worth it.
