I checked the etymology of that word and according to wikipedia.org – it was first used in 1946. Check out the article here. My guess is that the books of the 1940′s look differently than they do today. Today, there is a ton of time spent on the cover of books. I’m sure the books of the 1940′s didn’t have jackets and covers and probably not as much color as we have today.
Today, we judge everything we see by it’s cover and sometimes by it’s lack of covering. The sayings says that we should NEVER judge a book by it’s cover. Well, how about we change it to you – you can judge a book by it’s cover, but the way you judge it says something about you – not the book.