>> Considering the number of fingers that may have touched a telephone book during its manufacture and distribution (surely the cops have phone books and knew they weren't sent in the post, or if they had found a post worker's fingerprints on a piece of mail they wouldn't have arrested the postal worker) it seems to me that they may have been reckless in their conclusion.

That's why such evidence is supposed to be supportive of a larger case. Of course there will be a fingerprint on almost any given item. If you have a complete biometric database of every person in the country you will be able to match it, but that doesn't mean anything at all. If the person matched happens to be local it still doesn't mean anything by itself. In this case there was a plausible innocent explanation of how it got there, but in most cases people won't know how they spread their prints or DNA.