Over at GameOgre there’s an article about World of Warcraft’s Starter Edition accounts and what they mean for Activision-Blizzard as a whole. Also, they answer the question as to why WoW didn’t just go all the way to free-to-play with their offering.
Easy answer: spammers and gold farmers.
The long answer is a bit more complex, but it still boils down to the same distillation.
Link, via GameOgre.