There is a key difference. Those limitations of the physical books which you mentioned are inherent in the book itself. I.e. there is no way to implement a downloadable physical book and etc. Limitations of the DRM / vendor locked in ebook aren't inherent, they are imposed by interest of the vendor (Apples interest in the market share for their devices in this case). I.e. there IS a way to implement ebooks in another fashion, which won't limit interoperability and will promote more choice. But Apple is knowingly pushing worse approach, that's why it should be criticized.
