+1 to what avantman42 has just asked. I still don't get your point, which is why I half-jokingly asked in the first place if this is another of those "Amazon is evil threads"? I don't see anything other than how this is a good deal by Amazon - not one I'm interested in as I don't listen to audiobooks, but still a nice offer.
Would you walk into a shop and complain that the ticket price on a jacket says you have saved 20%, because you haven't bought the jacket so therefore haven't saved 20%? Or if you'd bought a pair of shoes and it said you could buy some socks for half price and save 50% you'd complain because you haven't bought the socks so not saved anything?
Edit: ignore this, I get your point now having read the replies and reread your post, you are complaining
just about the mathematics of the savings, albeit wrongly!