On the Kindle I use a larger font, so the OP does not show the book comparison which is relevant for my case.
Also, the Kindle largely replaces my newspaper reading. And the OP does not show the newspaper comparison.
Also, a lot of what I read on the Kindle are essays sent from places like longform.org to my @kindle.com address via readability.com or klip.me. For these the comparison is not with a paperback book page, but a computer screen. The computer screen may look better, but is uncomfortable for long texts.
Also, I sometimes read, on my Kindle, Gutenberg books that are locally unavailable in paper. Then the comparison would be a Kindle with nice large readable text on it, and a closed paperback