I'd agree with that definition on the whole. "Pure" sic-fi, to me, is about whether or not the basis of the tech could be based in an actual future reality. Most of the physics, for example, should be at least possible, if only in distant theory. But most stuff labeled as sci-fi isn't like that, with tons of fantasy elements thrown in all over (Star Trek...) so as far as how most people/business tend to use setting to define. I think it's because 'fantasy' is too all encompassing and things get divided into sub-genres for ease of labeling.
I consider most horror to be a sub-genre of fantasy.