Perhaps it's just a cultural difference; after all, there are so few American cultural institutions that permeate American society to the degree that apparently the BBC, some national/local newspapers, and a few literary prizes do. Maybe the university systems there do not possess the MFA/Creative Writing subset which champion a growing variety of narrative modes. Possibly, there is less admixture of writers who value experimenting with their texts; it is hard to say being more than 3,000 miles removed from the UK scene.
What does seem clear is that the debate there seems to be centered over who "drives the car" of fiction production. While there is the occasional outburst here in the US (I am thinking of the ridiculous io9 complaint about last year's "20 under 40" list produced by The New Yorker; read the 20's profiles and their authorial influences/favorites and then read some of their fiction and see why I view the io9 article so disparagingly), there also appears to be a greater willingness among the publishers and authors to write and publish works that reside equally comfortable in literary journals or genre magazines. This is not to say there isn't a perceived divide here, but rather that any such perceptions are generally fuzzier, likely due to a growing number of "cross-genre" works which are either finalists or winners of major awards.
If anything, the "purists" in most of these debates, or at least based on the American voices I've heard speak on this issue, would be those who are so committed to writing SF that they cannot accept a broader range of narratives that might fall within that category (or, for some, stories that contain SFnal elements that might be championed as also being part of other literary traditions). More and more lit journals in the US have published stories that are certainly speculative in nature and which utilize several tropes commonly associated with speculative genre fiction. I do not know if the same is occurring in the UK and is just being drowned out by the droning whines on either side of that silly perceived literary divide or if the literary climate there discourages such "cross-talk" within narratives.
All I know is that what I'm seeing linked to these days from the UK is rather baffling. Maybe I'm supposed to choose a side or something, hell if I know.