They did not. You misunderstood what was sold. One does not purchase a copy of OS X software. Apple does not sell the software. One purchases a LICENSE to run a specific version of OS X on an Apple branded computer under specific limited conditions, nothing more. Apple provides a copy of that version for you to install it on your Apple branded computer. You do not own that software; you own the limited license to operate the software. under that license.
Another bastardization of copyright. Imagine you don't buy a book at the book store, but instead purchase a LICENSE to read the book under very strict terms. It's idiotic. Copyright governs both books and software, so they should be treated the same. "License not purchase" is simply an end-run around constitutional copyright and commercial codes.