The PDF file format was developed to keep every item fixed based on its absolute position on a page of set size. PDFs are wonderful inputs for a printer.

Reflowable "ebook format"s like ePub were developed to let content "flow" into a screen of whatever size was available with no correspondence to any "page" idea. ePubs are wonderful inputs for reading systems.

Open a PDF, reduce the size of the window, all you get is the top left corner. There are the same number of pages, you just see a portion of the first and need to move your magnifying glass around the page to read everything (bad).

If you instead opened an ePub file and reduced the size of the window, the content would become narrower and longer, but all you'd have to do more was to scroll/advance through the content (good). This is no different than your web browser.

In addition to being more device-agnostic and reader-friendly, ePub files can also be vastly more accessible, convertable, and reusable than PDF.

Yeah, we (O'Reilly) are so committed to the ePub format winning the war that we threw up 262 more ePub-available titles on Tuesday and now have more than 400 available. See http://www.epubbooks.com/ for other publishers (there are starting to be a _lot_).

You wrote:

Secondly, the serif font selected (whose name does not seem to be identified in the book - a common practice ages ago) has quite thin curves, which arguably does make the font face more stylish, but diminishes readability.

And yet the last part of the entire book, the Colophon, where these things go, says this:

"""The cover font is Adobe ITC Garamond. The text font is Linotype Birka; the heading font is Adobe Myriad Condensed; and the code font is LucasFont's TheSansMonoCondensed."""