There are about 75-125 WoW servers (parallel instances of the game all hosted by Blizzard), each having several thousand to the low tens of thousands of users.

There are about 75-125 WoW servers (parallel instances of the game all hosted by Blizzard), each having several thousand to the low tens of thousands of users. 2056 GMs for that puts it at about 20-30 GMs a server. 20-30 people to police ~15,000 players seems reasonable. If a small percentage of people are having billing issues, that's tens of thousands of people with issues, and billing requires detailed, one-on-one interaction from a Blizzard employee, so 340 to handle all that seems reasonable to me. Based on the size of the player base the numbers seem right. The support staff will have to grow with the userbase.