J K Rowling will have a new book in September. I saw the pre-order tab on Amazon and then it struck me. The reason I pre-order a book is to be certain I get it as soon as possible. That being said, I very rarely pre-order a book.
The Kindle removes any need to pre-order. I pre-order out of a mixture of impatience and concern about availability.
An ebook is effectively available in infinite quantities and is available immediately upon release.
That means the only reason to ever pre-order an ebook is to lock in a good price.