There isn't ONE answer.
The German answer for splitting up the pie on books involves explicitly treating books as both market objects and as cultural things, and then identifying publishers, in particular, NOT authors and definitely NOT retailers as the people who are Creating Culture. I really cannot emphasize this enough. Publishers believe that they take dross from authors, make it Culture, and then retailers and distributors handle the messy market bits involving getting it out to us schlubs who need to be cultured (they apparently think we are yogurt or something). Publishers actually kind of universally believe this, but in Germany, it is Enshrined.
While publishers decide what kind of cut the retailer and distributor get, they cannot just say, you get nothing, because nobody requires the retailer to carry their books. Which honestly, at this point, I am a little surprised at. I foolishly believed that you never really, as a business, HAD to carry a product you didn't want to, and then R. pointed me at a long-standing and further delayed case involving a pharmacy in Olympia, WA, Plan B, and the state Pharmacy Board. That case sort of weirds me out (I'm all in favor of Plan B -- that's not the issue), but on balance, requiring all Pharmacies to carry the full formulary doesn't seem nuts to me. Requiring a bookstore to carry all books DOES seem kind of nuts to me, but if you showed me evidence that Germany did that, I'd shrug and go, "Germans". In any event, the retailers get something.
And obvs, a powerful retailer can have some impact in the cut "given" to them by the publisher. German antitrust law has spent my entire life struggling with this kind of negotiation issue over in food retailing, and the perversions of market definition they have engaged in really boggle the mind.
What seems to be happening right now with Amazon, Bonnier and the Börsenverein is a power struggle over the cut a retailer gets for ebooks. Amazon wants the cut for ebooks to be the same as the cut for pbooks. Historically, they've gotten LESS of a cut on ebooks than they have on pbooks, at least if The Bookseller is to be believed (if anyone can find me the full Amazon response, I'd love to read it).
"The Börsenverein claimed that Amazon was seeking to increase terms on e-book sales to the retailer from 30% to between 40% and 50%."
"In the UK, publishers have told The Bookseller that they too are facing tough negotiations with the giant retailer, with Amazon seeking parity on trade terms for e-books and p-books, and the ability to POD title where a publisher has run out of stock, or is having delivery issues."
" In a statement Amazon said: "We would like to present some local context: it's generally accepted that e-books should cost customers less than the corresponding print edition - in digital there is no printing, freight, warehousing, or returns.
“We believe that this fact should be reflected in the terms under which booksellers buy their books from publishers, and this is the case in our terms with most publishers around the world, including in Germany. For the vast majority of the books we sell from Bonnier, it is asking us to pay significantly more when we sell a digital edition than when we sell a print edition of the same title.""
Where I come from, if one person cuts the cake, the other people get to pick which piece they want first. I don't know how Germans do things, but if publishers get to make these decisions with no feedback from retailers? Why would anyone in the US side with _that_ approach, much less argue that Amazon's refusal to meekly accept these terms is somehow a good justification for indies in the US to side with TradPub in fighting to stop Evil Amazon from Asking for More?
I'm chalking it all up to confusion.