I think the international appeal of SF is quite understandable since the kinds of people who like to read it, are, by the nature of the beast, interested in other cultures, of which other nations on Earth are the closest available example.

And, of course, some SF is set close enough to here and now that Anglo and European do apply. Since many of the writers come from those backgrounds, so does much of the fiction.

As for sticking strictly to presently known science, I will simply point out that we have already experienced at least two major revolutions in science in this century alone.

Stanley Schmidt Quotes