an ePub book is basically a zipped HTML folder with static pictures and text. A 18 year old kindle can still render it easily. I expect Amazon are adding a lot more DRM and hoops than required. I also noticed if you havent read a book you downloaded for a while it wont let you read it again without re-connecting. Just glad I pulled everything onto my PC and Kobo a few years back. Agree the PC interface is pretty crappy though.