Is it really that different? You can think of it as an app that shows information you can navigate. It just needs a runtime e.g. pdf viewer just like apps need e.g. java runtime.
That’s an interesting point, because I guess nothing stopping an author from publishing their book wrapped in an ereader app and getting the commission discount, although they lose some of the market discovery benefit. Different contexts and ecosystems. The tech behind it has very little to do with the business/production and user end use.
I think some religious books are actually delivered this way and are quite successful.
Yes it's quite different. It's a deliberate platform lock in. Its pervasiveness does not make it the same as alternatives, it's far worse.