Here's here's proof that you don't truly own that digital book that you bought.
I'd always assumed that a digital book would be 'downloaded' to your computer.
Well, it is true, some digital books can be downloaded to the computer. For instance, I can go to Project Gutenberg and download a pdf. the problem with Amazon Kindle and some other proprietary formats is that it can only be read through their software. it is downloaded to your computer but only accessible through the software and they do have access to remove it at any time.
That's awful, i see what you mean, that's not 'owning' a book, merely allowing someone access to it.
I read something similar several years ago when the relatives of someone who died tried to claim the person's Kindle downloads and Amazon denied access stating that downloads are non-transferable.
As Yoko said to John:
"Oh boy when you're dead
You don't take nothing with you but your soul, think"
And access to your Kindle purchases it seems.