I suspect it's a perception issue... the price difference between a slim programming book and a fat one is minimal. Dropping $50-$60 on a tome feels like a better value if you have to wheel it out with a dolly, instead of slipping it in your pocket.
I have to concur, unfortunately. If a tutorial book adds a huge reference section, I'd feel that it's a better deal for the same price- I may never look at the appendices, but I'll feel that I possibly could, just in case. Publishers ought to fix the pricing in general.
