It is of course certain someone at Apple had seen Delicious Library, and likely one of the people who had seen that design were involved in the original iBooks. But there is no functionality overlap with Delicious Library - DL was about cataloging media and managing loans, not accessing digital media itself. I was not able to add a digital book or movie to DL, nor could I make a reference to a physical book or movie I own in iBooks.

But its also not like there were that many skeuomorphic UIs for managing books. Actually two - a bookshelf showing spines, and one showing fronts. And if you are going to maintain a picture of the front, you're probably going to want to show it by default.