See http://chicagotribune.com/features/lifestyle/chi-0201160110jan16.story?coll=chi-leisure-hed for a different take on this. The article stresses that plagiarism harms the reading public -- which is my position you misunderstand me here, CK -- but the article's reasoning is different from mine and IMHO is somewhat fatuous.

Nobody got hurt, right? Well, actually, that's not right.

There were a whole lot of victims -- and not just the historians whose words Ambrose plagiarized. As trite as it may sound, everyone's the loser when a writer, particularly a historian, such as Ambrose, takes the lazy way out and copies someone else's words, perspectives and ideas and presents them as his own. What's lost, at that moment, is an opportunity for a new insight into -- a fresh way of understanding -- the human condition.

As to Ambrose's particular case, the article struck me as a reasonably thorough and balanced discussion.