> they're unlikely to systematically prefer newer editions

That seems wrong to me. Generally when a new edition of something is put out it's (at least nominally) because they've made improvements.

("At least nominally" because it may happen that a publisher puts out different editions regularly simply because by doing so they can get people to keep buying them -- e.g., if some university course uses edition E of book B then students may feel that they have to get that specific edition, and the university may feel that they have to ask for the latest edition rather than an earlier one so that students can reliably get hold of it, so if the publisher puts out a new edition every year that's just different for the sake of being different then that may net them a lot of sales. But I don't think it's true for most books with multiple editions that later ones aren't systematically better than earlier ones.)