Yes, the lithographs are "listed" in the book with a description of each of them (no photos though). However, no prices are listed for them, because as you mentioned, they alone, rarely appear for sale without the cars. A few months back, there was a few GNX/Doble prints available (by themselves, no cars) on Ebay that sold in the $60-$80 range.
As for the cars themselves (mostly without the lithos), they appear regularly on Ebay, which is where most of the pricing for all of the cars came from. Hence, "actual" values.
The book is really meant to be used as a "reference" guide (good "checklist" too!) for all available collectible items concerning the turbo regals, not necessarily a "price" guide, even though it does have prices listed within for what a lot of the items have recently been sold for.
Hope that helps explain things a bit.