Following my advice (just kidding), Sir Bruce updated his MMOGChart.com website with the latest subscription numbers of MMORPGs.
May I draw your attention to the market share chart, which shows over 50% of MMORPG players being held captive by World of Warcraft. Another graph on market share by genre shows 92.6% of players being in a Fantasy MMORPG. Given the much lower market share of Fantasy in other forms of entertainment (books, TV, movies), this suggest the market is ripe for games exploring other genres. Fortunately there seem to be more Science Fiction, Pirate, and Historical themed MMORPGs announced nowadays than Fantasy.
I still wonder if Fantasy inherently makes better MMORPGs, or whether it was just an accident of history, coupled with the natural desire of game companies to clone instead to innovate, which leads to this crushing dominance of Fantasy in the market.