Yahoo (Google's competition) has a note about non-profit publishers who protest against Google scanning of library material.
They say that it can lower their sales. If they want to keep their current business model, that's probably true. If they want to change... Well..in the Net they have a possibility to get to many more customers, especially when they publish rare, hard to get books. For me, they can get even bigger sales this way.
Another argument is that Google breaks copyright law. I don't believe such a big company can do it so directly. It'll be interesing to see how it progresses.