Three isolated examples do not a consensus make. Again, I ask for one study/report that shows a majority of US libraries have moved away from Dewey for non-fiction. I'll wait.
My point is that the mere fact your "wife" hasn't mentioned the term "beach fiction" or "beach novel," does not mean the term isn't widely used. I once dated a dentist. She talked about her job frequently. That did not mean I was 100% knowledgable about dentistry simply thru osmosis. Similarly, there may be terms used in literary circles or a library that you are unaware of, despite the fact you may or may not be married to a librarian.