Amazon Kindle books sometimes receive ebook updates that the publisher or author pushes out. The Amazon Kindle e-reader has a reporting feature in digital books for spelling mistakes that are automatically sent over and often revised. The ebook cover art will be updated to generate interest when a book is made into a movie. An example of this is Andy Weir's The Martian; the old book was orange and had an image of an astronaut, but the updated one has a massive face of actor Matt Damon. Amazon is not the only company to update ebooks; Google Play and Kobo
Since there’s a case to be made either way, it would be nice if the publishers could offer two editions and let the reader choose. This might be too expensive in the case of printed books, but for e-books it seems like it should be feasible.
Sure. These things are products to be purchased, after all. Regardless of how you feel about the content of the books themselves, I’d be extraordinarily annoyed if a company could just edit on a whim the content I had paid for and expected to have in perpetuity. That said, you should never realistically buy anything from an online publisher that doesn’t let you save a static text copy of the book as a PDF or other file offline. More generally, if you want to buy a book, the best thing to do is to buy from a used bookstore, if you’re able. Not like Amazon needs any more money.