Is Earth Abides Science Fiction?

This question was in play when Stewart's novel first came out in 1949 and it's one I'm putting in play for us here.

Think of all the other novels, films and tv shows, and more that are definitely post-apocalyptic but may or may not be science fiction: recently, Cormac McCarthy's The Road or Brian Vaughan's comic book series Y: The Last Man; not so long ago, Stephen King's The Stand or the tv show The Day After; roughly contemporaneously with Stewart, all the authors Connie Willis mentions in her 2005 introduction to the new edition. Which would you consider science fiction? Which not? And why?

Just to get us thinking about defining science fiction, why we do it, and what's at stake in it....