Very likely, yes. Though what fandom does seem to latch onto are apocalyptic stories and AUs. However, I agree that the endings tend to be hopeful, with the main characters or couple surviving, even if other characters die.

Stories that buck the trend tend to be memorable though. I recall one Buffy fic that reworked an end-of-the-world novel or movie (I forget now) and the ending was powerful enough that I've never forgotten it.