It's almost sad the OP has no grounding in reality whatsoever.
Agreed, and one of the realities in which the OP has no grounding is the technical reality.
Games like Battlefield 2 require almost no database capacity on the server side. Private servers require no database at all. The account servers use databases, but keep only a few bytes of information per character and read/write it infrequently.
A game like World of Warcraft requires truly massive online database capacity, at very high transaction volumes. Much of the world is persistent on the server side: objects are persistent, players are persistent, NPC are persistent, etc., etc.
Let's talk capacity. Assume 25% of the 5m subscribers of WoW are playing at any one time. 1,250,000 people online.
Without getting into specifics of how often the game reads the database for any particular client (i.e. if you are standing in an empty wilderness not moving, then it would only have to read every second or so to detect objects moving into your clipping envelop), it's fair to assume a capacity requirement of 500,000 to 1,500,000 transactions per second, with mean response times < 50-250 ms.
Bandwidth: fair to assume that WoW requires a 32 kbps stream, with higher bursts. You're looking at 48 million kbps. That's something like 38 gigabits of bandwidth. Or really, 76 gigabits, since you need redundant pipes.
What about hardware? Oh boy, they need some hardware
Datacenters to house all this stuff? Kinda expensive. Air conditioning, generators, people expect these games to be as reliable as Citibank's applications.
Business infrastructure to support it all? Haha. The OP clearly cannot imagine. I don't know Blizzard's monthly overhead costs, but an educated guess would be... umm... bazillions.
So good luck with those free WoW servers