Gidge, thta's my point about the internet. You can obtain all more than enough material that will give you the basic structures of a song and detailed analysis of each section, coupled with does and dont's-that's all free. Why then would you want to buy a book that gives you a very narrow opionion of songwriting.
I'd think about buying a book if it was written by McCartney, Dylan, Reed, Cohen................all about songwriting, but I bet there would be very little suprises even then on their methods. Buy their autobiographies instead and you'll see about where they came from. That is the biggest factor concerning songwriting in my opionion. Who they were, what/where they grew up around, who they met and then if they could still hack it when they made it into the big time.