a genre that uses magic and other supernatural forms as a primary element of plot, theme, and/or setting. The genre is usually associated with the overall look, feel and themes of the European Early Middle AgesWhile Science Fiction is:
a broad genre of fiction that often involves speculations based on current or future science or technology.Chalk and Cheese right? So how come the same people read both? We are not talking about co-incidental liking here. The correlation is so strong that many bookstores have a single section called "Fantasy and Science Fiction". A quick Google search will confirm that fan-sites likewise combine the two apparently different themes.
I don't really know why the links are so strong but I guess it has to do with the fact that they both describe imaginary worlds. As good an explanation as any can be got from 42explore.com :
All science-fiction and fantasy writers face a common challenge. They try to present worlds that are radically and intriguingly different from today's world.And yet ... If it is all about imagination and "what if..." why are successful fantasy novels so formulaic?
Of course it goes without saying that the same people who enjoy F&SF are also a pretty likely candidates to enjoy mmorpgs but that is an easier link to figure out. Mmorpgs allow players to directly participate in fantasy or science fiction worlds.