For a game company to stay in business, they need a source of income. Mainstream games have relied on sold copies to cover the costs of development and support, and that worked well for a while. However, an MMORPG title has additional expense, most notably caused by the servers and support team to keep the game running. Developers have created a number of strategies to generate revenue to cover these costs, and make startling profits.
The typical means of profit for MMORPG developers is in the monthly fee. In World of Warcraft, you have to buy the base game, which comes with a free 30 day trial of the game. For each additional month, you have to pay $14.99. Not only is Blizzard getting $40 for each copy, but they're also getting $15/month per subscription. With their player base in the millions, that's a considerable sum, and one reason this method is so popular.
A second method comes from the earlier concept of games: Pay once, play forever. Guild Wars is the only title that comes to mind that is actually an MMORPG. The benefit is that you can charge more for the main game and expansions, and players will put up with less content, because it's "cheaper." You lower costs, and have no real incentive to keep players playing the game. Works great if you think your MMORPG will go out of style in a few years, so you curtail the cost of further development and setting up a lot of servers.
Those are the two main forms of MMORPG revenue. These are used by mainstream developers and make good, steady profits from them. Tomorrow, I'll explore the non-traditional methods of MMORPG Revenue. Most of these involve a freely available base games, so if you're looking for free MMORPG fun, stay tuned.