I understand the point of the article to be that it's interesting when artifacts evolve and previously functional elements are retained for a purely decorative purpose. I take your point to be that it's not so interesting.

Consider that a typical Kindle contains dozens of books, so it is more like a bookshelf than a single book. The original design intent was for the device to "get out of the way and disappear so you can enter the author’s world." The display may have a page-turning animation, or a dog-ear icon indicating a bookmark, or adjustable margins, but outside of the reading interface I don't see book-like structural features, certainly not a spine to hold the pages together and display the title while the book is shelved.

A cover is a functional accessory "to keep clean and avoid problems with the screen" and not a merely decorative replacement for a formerly functional element. Hardback books have dust jackets that also have a functional purpose: to protect (and decorate) the book.

I don't see the relevance of the floppy disk or save button. Storage media has evolved considerably, from flexible plastic disks to hard platters in metal enclosures, shiny CD-ROMs and DVDs, and now solid state flash memory. At no point was a previously functional element retained for decorative purposes. The GUI happened to become popular when the 3.5-inch disk was in service, the save button adopted that image as an icon and has not evolved since.

The OP said that.

Indeed, that must be why I was looking for dentils in my photo, but I forgot by the time I got to the nitpick-Devac stage. "Vestigial" is probably a better fit, but it implies uselessness so maybe we are stuck with "skeuomorphic."