[Quoth]

I doubt there is any "house brand" that has the uniqueness of a particular book.
Any "house brand" is simply a version of a widely available product. It might be slightly different due to quality, but it's not a monopoly product.

An Amazon imprint title is otherwise totally unavailable. There will not be a single chain store "house branded" item that doesn't have a close enough equivalent. A detective book from Author "B" published by Penguin is not an alternative to a detective book from Author "A" published with amazon, it's in addition to, like you can buy carrots and peas.

You might as well say it doesn't matter which film, book, or music you consume. If someone wants Taylor Swift giving them Shania Twain or Dolly Parton won't do. You can't say it doesn't matter if your favorite singer is on Spotify and you have no internet, or you don't want to sub just for one artist.