<<They aren't. The "real" version of the book is the scanned image. The ePub version is just a "quick and dirty" OCR of that. Download the image version if you want the real thing. Harry>>
As I wrote earlier - the pdf version is just fine on a computer.
We're talking e-readers here. If you put that huge file in a PRS-600, you find a couple of unfortunate things: it's very slow to change pages, & in mine it can freeze the e-reader, and it will not magnify the original page. That's a waste of everybody's time. While the ePub version is "quick", yes it is so "dirty" it's not worth looking at. Another waste of space and time, that is simply embarrassing on the Internet Archive.