One thing that I do find interesting, is that the book (on text processing, no less), that is 680 pages x 30 lines x 80 columns (plus some minimal line art) - which, in theory, is around 1.6 megabytes of data, weighs in at 28 MBytes in this PDF.
Regardless of the Irony, great book which the authors clearly put blood, sweat and tears into.
http://oreilly.com/openbook/utp/UnixTextProcessing.pdf
has _scanned_ pages with text layer on top of it. That's the reason why it's so big.
I applaud retyping effort, as it's always better to preserve real content than images of it (even if OCRed), but I cannot say that I'm happy about troff being used for this purpose. It can be a matter of taste, but I don't like the way formatting is done in troff/nroff. That's why I never use it directly (e.g. using ronn to convert markdown text to man page, etc.).
But I understand it's done that way to preserve "the creation process" too, which is also appreciated. And the book is about troff/nroff, so dogfooding is present. ;)