The worst thing is that it's entirely possible his contract with the publisher is structured in a way that if he makes the book available as a free download or sells it on Lulu.com, the publisher will unleash their lawyers upon him.
I have a single correspondence with the author about compensating him for his effort (I used the online edition) to learn lisp and he refused -- as the publisher has first rights to collect monies on the book -- , I am inclined not to even fleetingly question his judgment in posting the book online.
OTOH, he could make a second edition and start selling that, if the agreement with the publisher allows.
Unless the contract is deliberately convoluted, it shouldn't take more than an lawyer x hour to sort that question out.
I had the idea of a more booklike PDF.
I wonder if the author would seriously object to that.