Crooked Bee
(no longer) a wide-wandering bee
The differences are more than digital vs physical. In fact, that is an (almost) irrelevant distinction from that perspective. The problem is you don't understand what a pdf file is and are looking at the issue from a completely wrong angle (fuck you IDtenT, you ninja!).
Think about what happens when you resize a book, a book in pdf format or the browser window. What distance are you reading your book/pdf/web site from? What size is the page/window/window? How big are the fonts in each case? Are you leaning back in a chair or sitting straight? Now work from that.
Most differences are subtle. It adds up and readers just don't feel as comfortable reading the text. It's not a huge problem, but it is a problem. A problem that is not difficult to address and a problem that the "person partly responsible for the editing" should address (with something other than a couple of retarded posts). Acknowledge the criticism and bring it up with DU. It's cool. No one is expecting you to do anything more.
Eh, I wasn't talking about reading being "comfortable" or not at all - it's pretty obvious that's individual - and I thought you didn't either. I think we're talking past each other.