In a review for Strange Horizons of The Secret History of Science Fiction, Paul Kincaid writes
In other words, for one group science fiction is a set of tools to be put at the service of the story, for the other group science fiction is a way of telling story, and this difference, though subtle, is significant.
I'd have to read all the stories in the collection to be sure I agree with exactly what he's getting at, but it's worth pointing out, since the collection under review is looking at cross-pollination between stories published obviously within genre and stories published by writers generally regarded as mainstream or literary, that he's not dividing the stories along those lines in this quote. Admittedly, he finds the ostensibly non-genre stories more likely to be in the first group and the SF stories more likely to be in the second, but the categories are imperfect predictors...which is largely the point. The borders and boundaries are fluid (and me, perhaps I aspire to be an undocumented immigrant across those lines...).
To expand on the difference he sees, here's another quote: "In the main...the devices of science fiction are being used as tools with which to question what it is that makes us human." This is completely in line with essays and quotes from Ursula Le Guin that I've mentioned here before, and definitely reflects my thoughts on speculative fiction in general--the fantastic can be cool or uncanny or horrific, full of a sense of wonder or dread, but that's not the purpose in itself. The point is to journey from that sense of whatever back to finding those same things in the real world of today.