So the last things I bought through Amazon:
- Advances in Automatic Text Summarization, edited by Inderjeet Mani and Mark T. Maybury
- OpenGL Insights, edited by Patrick Cozzi and Chrishophe Riccio
- Three Rival Versions of Moral Enquiry: Encyclopedia, Genealogy, and Tradition: Being Gifford Lectures Delivered in the University of Edinburgh in 1988, by Alisdaire McIntyre
- Calendrical Calculations, by Nachum Dershowitz and Edward M. Reingold
All were eligible for Prime. None of them are particularly obscure books, but they're not 50 Shades of Grey either. Only one is available on walmart.com. At one point I was a pretty typical Amazon customer. I'm willing to believe the typical Amazon customer has changed, but I still don't buy that they're interchangable services.