Don't be obtuse.

I own a physical book, I don't own the IP of it. As long as I own the book - I can freely read it's contents 100 years from now.

If I own[1] DRM protected ebook on a Kindle. Tomorrow I may not have that book on my Kindle (and I will not be refunded, because fuck the plebs) or may not be able to open it even if I have the file, that I bought with my money.

[1] I paid money for it, just like the physical one.