Are Short Stories Scientific?

I was at the bookstore today, in the SF/Fantasy section as usual, looking at the anthologies that are lined up between "New Books" and the A's. They were all science fiction.

As I thought about that, it occurred to me that almost all the sf/f short story anthologies I'd seen were science fiction rather than fantasy. Fantasy, on the other hand, seems to have all the super-long Jordan/Goodkind epics.

Why is that? Is it just a quirk of publishing history- i.e. if Jordan had been an SF writer, we'd have a lot of encyclopedia-length science fiction imitators? Or is there something in the vaguely-defined difference between the two that selects for story length?