T’re not, really. Digital (e-book) sales did grow quite sharply and suddenly when t first appeared. But in major markets like the US and UK, the recent trend is for a slight decline in e-book sales and modest growth in sales of printed books. Now…I think (subjectively) that it may be true that people who in the past would have had just a few books now have even fewer, or none. For example, if you weren’t really a reader but you felt you ought to own a dictionary and an encyclopedia for the kids…well, that’s now not necessary, because you can get the same information online. So (I’m speculating here, I don’t know for sure) it could be that the total “prevalence of book purchase”, in other words the number of people who have bought at least one printed book over a certain time period, has declined. And this could give the impression that books are becoming rare. But in fact, t’re holding their ground against digital pretty well, in terms of overall sales. It’s also true that small independent local bookstores have suffered very badly in the last couple of decades, with many disappearing. That, again, might seem like a sign of “the end of the book”. But really, that’s down to broader trends disfavouring small independent retailers, and also down to the ease of online ordering. It may have killed off many little bookstores, but Amazon’s ordering service has probably done more to keep than the printed book alive than its e-books have done in damage!
When it comes to format, you don't want to let your readers adjust the formatting to their preference. Because then the reader will adjust its book just to suit their preferences, and then you have to adjust to that in your book. The reason for that is you want to keep it, so you can easily adjust it with your reader. So you need to make sure, once your book is finished, that your reader can easily adjust to that. Therefore, the key here is to keep your formatting simple and straightforward. In addition to that, you want to provide as much info that your reader could use so that the reader finds out how to use the info in one go and not have to do more work if they do not understand everything. This includes everything from information on how to change the book, to how to download and read it,.