One of the first space games I remember playing was Sierra's Space Quest. I took on the role of ... *ahem* Sanitation Engineer in what I assumed to be a distant future where space travel was the norm. I escaped the hostile-alien-overrun ship, terribly dismayed at the now bloodied state of my once clean floors. Damn aliens. I made my way in my escape pod to the desert planet, and quenched my thirst on the evaporated water when I got thirsty. Hey, it could happen ... it's the future.
See, that's the neat thing about space games. Because our own experiences are the lens through which we view most things, space games are inherently the future. Yes, we've made tiny little forays into space, but certainly nothing so great as to require a Sanitation Engineer as part of the crew. One might say we've made baby steps into the infinite possibility that is space, and that perhaps the future holds more.
Other genres, well, I can't prove that there ever were elves or orcs. I can't prove the Missing Link (it is "missing," after all) either, but scientists seem bound and determined it existed. And some of those same scientists found remains of a dwarf-like or hobbit-like species not too long ago. So, while it may be improbable, it's still possible the denizens of many fantasy realms did once inhabit our world.
The point is, they are not inherently future, and therefore not completely open to possibility and interpretation in quite the same way space is. Space is fertile ground for, well, anything. Especially games. Which is why we have devoted this week's issue of The Escapist, "In Spaaaace," to games set ... in space. Allen Varney writes in about one of the most beloved space games of all time, Wing Commander. Adam LaMosca travels through a brief history of space sims, recounting some of the ups and downs over time. Also, Shannon Drake talks with the members of EVE Online's development team at CCP. Find these articles and more in The Escapist.