Science fiction magazines as innovators?

I’m reading The Cambridge Companion to Science Fiction, a collection of deadly serious essays aimed at an audience aware of, but not that familiar with science fiction. It includes the usual history of the genre and the chapter on the sf magazines ends with the following statement:

A magazine was like the small independent film as opposed to the Hollywood blockbuster, which has to meet the expectations of the broadest possible audience. Magazines have subscribers and more-or-less guaranteed space on newsstands. Books must be promoted. Even now, well after the heyday of the magazines, most innovation within the field takes place in the remaining magazines or in their contemporary equivalents. The latter include small press volumes, semi-professional publications and on-line publishers.

In the first place does this analogy not hold water. Written science fiction in any form is a niche market; a profitable niche market, but still small peanuts. To compare any book publication to a Hollywood blockbuster is just absurd, as the pressures on a science fiction book to perform well are several magnitudes less than they are on even a “cheap” Hollywood film. This comparison is needlessly disparaging.

I consider myself reasonably well read within the genre, but I do not see the innovation within magazines that is supposedly not present in books. The best modern sf writers, like Iain (M.) Banks, Ken MacLeod, China Miéville, Liz Williams, Lois McMaster Bujold or Jon Courtenay Grimwood, started primarily as novelists, not short story writers and skipped the magazines more or less entirely. In the last five years or so I can only think of Charlie Stross as a writer whose reputation was largely made through his short stories.

Looking at the magazines, or at least at the various Year’s Best anthologies I do not see the innovation there. These anthologies should have the best in short fiction published in science fiction in a given year and should therefore particularly showcase innovative works, should they not? But looking at the stories published in them first seen in the core magazines (Asimov, Magazine of Fantasy and Science Fiction, Analog and Interzone) there are quite a number of good stories there, but nothing as gloriously new as the best novels of MacLeod, Banks, Grimwood, Williams, Stross or Miéville.

So am I missing something? Or was this just so much blather?