The OCR tech built into Acrobat isn't that advanced. The layout of a roleplaying game, the many non-standard words for gaming terms and monster and whatnot makes doing a correction of an OCR:ed PDF an ardous task, taking much more than 10 hours to clean up.
And, I not really sure Acrobat allows for editing OCR:d text in the PDF itself. As far as I know (I might be wrong) the text must be extracted before being edited, and after that reinserted somehow, although that is way over my skill level, if at all possible.
Basically, OCR is not a magic silver bullet to turn scanned PDF:s into squeeky clean text gaming books, as far as I know.
/M
The OCR I'm familiar with is in older science articles scanned for archival in online repositories. Lots of non-standard jargon words in there, and I expect that the people doing the scanning are probably not paid very well--RA salaries, most likely, although I don't know for sure. So it's not crazy to think that someone with a free weekend or two could crank out a professional-quality scan. At least, as professional as JStor is.
The thing is, if I wanted to, I could sit down and type out the PHB 2 in less than a day. Presto, I have a text document. If I were going to be clever, I'd do it line by line as it appeared in the book with returns at the end of each line. No OCR scan required, and I get the text right the first time. Then, assuming that the PDF software I've pirated is reasonably useful, I would just copy-paste or copy-associate the text line by line.
More than 10 hours of work, for sure. But if someone is motivated to produce a good pirated PDF, it's not unreasonable. I can't understand why anyone would want to both scanning in a whole book, clean it up, and assemble it into a PDF in the first place, but maybe I'm just lazy. Still, people do, and the difference between a terrible scan and a good one is simply the level of motivation of the scanner.
Not to mention that if the original scan was good enough (i.e. high-resolution), but not OCRed or bookmarked, someone else could just add those things and repost it. We could call it WikiPiracy. User-edited copyright infringement.