Hold on for a minute. WoW is almost the exact opposite of this model, and for that reason I still respect it as an MMO compared to others I've seen.
In WoW, at least when I played it heavily during the Lich King expansion, you pay for the game and for a monthly subscription fee and that's it -- there was no other use for real money other than maybe buying a faster computer or a vent server, but that's outside of the game environment. Buying gold, while possible, was heavily discouraged and bannable.
This policy made WoW feel very fair to teenage me and I ended up putting a considerable amount of time into the game as a result. I realized that it was plausible for me to be the best simply by putting enough time into it.
Additionally, WoW's social environment is typically what keeps the long-term players going (as opposed to ingame objectives, although objectives are important for keeping players engaged), and that's another story entirely.