There seems to be a sort of hierarchy of literary respectability in the sf genre. At the top are the recognized literary figures who write novels using sf tropes. Examples include Michael Chabon, Anthony Burgess, and George Orwell. These authors don't usually consider themselves sf writers, and sometimes object to having their works described as sf. That's because the genre is considered to be in some way disreputable, something David Barnett discussed in his article, "Science fiction is the genre that dare not speak its name."
Then there are the talented writers who cut their teeth writing sf, but who have gained a broader recognition. I'm thinking here of Ray Bradbury, Ursula K. LeGuin, Stanislaw Lem, Chip Delaney, and others. Relieved at having their talent recognized, some of them try to distance themselves from their genre launching pad. As Bruce Sterling once colorfully put it, they managed to "wriggle out, somehow, barely, gasping and stinking of rocket fuel." So now authors like Harlan Ellison declaim that they never, ever wrote science fiction, and Michael Moorcock insists that he finds spaceships boring.
Further down are the comic books authors. These are the Neil Gaimans and Alan Moores. The current faddishness of comics has increased their cache of late, but it's still the case that comics have an even worse reputation than most sf writings.
At at the lowest level we find the game designers who have turned to fiction. Here are Aaron Alston, Mike Stackpole, Ken St. Andre, et al. Regardless of the talent they display they write under the shadow of the aesthetic taboo that you must never novelize your RPG campaign (something they don't do).
Maybe someday we'll escape such stratification. As readers we should do our best to put our preconceptions aside and judge books solely on the artistic virtues the writer displays. This seems to be happening more often. Comic books have lost some of the stigma they used to carry; sf author Chris Beckett just beat out several mainstream writers for a literary prize; and Ryo Mizuno broke all the rules by turning his RPG campaign into a series of popular novels. So maybe the day is at hand when we can enjoy author's works based solely on their own merits rather than where they fall in an artificial spectrum.