Book sellers that group science fiction with fantasy follow Arthur C. Clarke's observation: "Any sufficiently advanced technology is indistinguishable from magic." Larry Niven pointed out the converse about sufficiently analyzed magic. I'd be interested in how you would rigorously separate these.
I understand what you're getting at: you're trying to avoid works of speculative fiction that take place in a so-called standard fantasy setting. But otherwise, it sounds like you're trying to distinguish "past" from "future". This is complicated by settings that are nominally soft science fiction but do not cross over with real-life history in such a way as to anchor dates. These include BSG ("All this has happened before, and all this will happen again" more than 150,000 years ago) and Star Wars ("A long time ago, in a galaxy far, far away..."). What opinion do you have about speculative fiction settings closer to the present day, such as "steampunk" (recent past) and "urban fantasy" (present)?
The other topic about translation, that is easy to answer: american copyright law is at fault. As it prohibits authors to sell their work as they please. Once sold to a publisher the publisher has 'the copyright'
What compels an author to sell permanent exclusive rights, whether through assignment or exclusive license, to a publisher?
I fail to see what your two points add to the discussion :)
First, I was clarifying that the convergence of science fiction with fantasy is not the fault of book sellers but instead the result of a fundamental continuum between the two. Second, I was clarifying that unavailable translations are not the fault of book sellers, be they Amazon or brick and mortar, but instead business decisions made by authors.