The thing y'all have to consider is that an MMO has to build up userbase. It hasn't been at 10 million since the moment it was released. It probably still is the most profitable, but the argument a lot of you are making isn't valid.
Another heavy hitter is Maple Story. It had 50 million players in Asia, and that was a couple of years ago (very popular in China). It's got a humongous userbase in the States as well. While it doesn't have monthly fees, it makes a ton on micro transactions. I believe it made 220 million the FIRST YEAR after its introduction (a very long time ago), and it's grown exponentially in popularity since then. Also, consider how little it took to create. It's a 2D side scrolling, sprite-based, MMORPG. Most of the cost of maintenance is servers, I'm betting.
If MS is making $16m/mo, that puts it in a very strong position, but WoW is making far more than that. Blizzard, in 07 (in which, WoW had a much smaller userbase) reported sales of $1.2 Billion USD for the year. That was with 7-8 million concurrent users (it's 11m now, FYI). That's nearly $100m/mo, and had profits exceeding $40 million USD a month. World of Warcraft hit $250 million USD a year in 2005. When you talk WoW players, you have to factor in:
- Boxed Product Cost ($20 a player at any store)
- $3-15 monthly subscription (varies on payment plan and location. Asia is cheaper, but the West charges upto $15/mo)
- Expansions (Another $20+ a pop)
- Ad monetization on Battle.net and other sites (I actually have hard info on what they make on this, but I don't think I can say).
Between it all, I wouldn't be suprised if WoW is bringing in between $150 and $200 million a month now. Maple Story is doing phenominal, but you have to consider that it's revenue streams aren't going to be as hot as a subscription based service like WoW.
Back from the dead, I'm afraid.