The Authors Guild immediately pointed out that books that are out of print sometimes come back into print, which I suppose is true for one book out of 100,000, but it's not much of an argument. A lawyer for the publishers cryptically said "It may be unwise to make any significant change in our posture" and noted that for older books it can be hard to tell if the publisher still has the rights.

Google's newly revealed emphasis on out of print books makes sense as a way to maximize the usefulness of their index, but it also makes sense as a legal strategy. If it came to a point of a settlement with the Authors' Guild or the publishers, an agreement only to scan books that are out of print wouldn't be a terrible outcome for readers and researchers. Books that are in print are a lot easier to find and to find out about, and a heck of a lot of them have opted into Google's publisher program anyway.