What they're afraid of in calling it sf is that people like my grandmother-- who loved it-- wouldn't even have picked it up. SF is a minority market, but TTW is better than what people expect from the SF shelves: and hardcore SF fans, who want science and only science with no charaterisation, like my brother, don't want this sort of well-written, elegant thing. It is SF, I agree; but it's SF which should transcend the narrow 'genre' thing which everyone gets trapped into, and so I can quite understand not wanting to label it that.

I enjoyed it, though it gave me the usual time-travel-logistics headache, especially when I started discussing closed-loop and open-loop time travel stories on b.org.