I learned from an industry pro years ago that there are only a small handful of base resin producers. All the retailers of epoxy products buy from them and add their proprietary additive packages to tailor the products performance - fast cure, clarity, mix ratios etc. etc.
This means there is...
Phil, you sound like a dummy - they wrote the book to pass on their acquired info and to make money - just like anyone who writes a book.
My copy cost $15 in the 70's - reasonable but not cheap.
Putting it on the Interweb for free was a goodwill gesture.
The Gougeon's literally wrote the book on boat/epoxy work.
To say, or even imply that they are whoring simply for sales is to do them a gross disservice.
Advances in techniques have come along since I acquired my first edition but it is still the most useful text on the subject.