Compare that to selling music on bandcamp: They take 15%, the rest is yours to keep.
It is absolutely beyond me, how self-publishing authors put up with that.
I GUESS the difference between music and e-Books, to some extent, is how the channel influences perceptions of the quality of the product. People have got very used to low quality writing being available for free on the web. So if your ebook is just another piece of text on some website, many people will not be willing to pay for it, whereas being on amazon creates an expectation that the quality would be in line with properly published work (where, at least, there is a four-eyes principle at work, at shouldering financial risks around a book project etc.)
Someone should do something about that and create an ebook marketplace that enforces certain quality standards and pays decent royalties.