Sufficiently complex HTML is copyrightable, thought whether any PG HTML reaches that level is questionable. However, anyone PPing for PG knows what they're getting into; whether legally they could object or not, it would strike me as a sleezy thing to do.
I've chewed on this for a while, and I agree with you that I think anyone submitting to PG has made a reasonably informed choice to allow PG to distribute the HTML book under the terms of the PG license. Given that that license also allows anyone to strip the PG trademark and the license and then do what they want to do with that book, seems to me that also allows PG to agree to work with Apple or whoever they want to distribute the book without the PG trademark and license. The remaining problem would be if PG describes that HTML as being "public domain." Maybe it is or Maybe it isn't. And it is probably not a good thing for PG to describe a work as being "public domain" if it isn't. This all comes down to I think, whether a legal authority would decide that HTML is "Printers Art" which simply describes the layout of a printed work -- which is not copyrightable IMHO, or whether that HTML is "Computer Code" which then would be a derivative work, and the added HTML of the derivation then would remain under the copyright of the HTML coder -- even assuming that the coder did give an implied license to PG to distribute the work under the typical PG licensing agreement. Seems like the problem could be solved if the HTML coder assigned any residual rights to the HTML code to the US Government for example. Or if the HTML coder agreed explicitly that it is a work for hire. Or, whatever. But again, I Am Not A Copyright Lawyer. [And Reading about Sonny Bono gives me a headache.] [[And I hate meeces to pieces.]]