Have you ever red the fineprint for Amazon Kindle?
You may have payed for its books, but you do not own them at all. If you take your Kindle to another continent, for example, and use the deiove there for trying to buy another ebook from one of the local Amazon stores there, Amazon reserves the right (and has executed that repeatedly) to delete your account at home and delete all your books ever bought. Books gone, money gone.
Enjoy living at the mercy of somebody else not pushing a button.
That is the biggest issue with digital sales, may it be software, may it be printware: private property is a term that has become useless there. You do not own anything for real with it. You cannot resell it. You cannot exchange or barter it. You are dependent and remote-controllable. And if the other thinks you "owned" something for long enough and that you should not own it any longer, or should not own this version, but an edited, different version of a book, there is nothing you can do - he does what he wants, and you suffer what you must.