They're not presenting the entire book, are they? I thought it was just short excerpts matching your search queries - essentially the same thing they do for (also copryighted) websites.
It's like arguing that a movie trailer gave away the best parts of the movie, so you have no need to watch the movie.
Well, what I got from such cases was not a summary of a book, but useful code or math or a technical explanation. Google book search can work like a reference library, and if it's really good at that then I can see how it might cut into sales.
For example, if someone publishes a cookbook (for food or code, for that matter) it seems possible that people could just search for the small-ish section they need and never have to buy that book.
In practice I suspect the number of actual lost sales because of this is minuscule.
If a $200 math textbook instead was published as a series of $2.99 chapters, students would be less likely to try to steal or avoid payment.
Most cases of piracy come down to distribution, delivery, and convenience simply being improperly aligned with consumer demand. Do people pirate Game of Thrones because they don't want to pay for it, or because HBO makes it too inconvenient and expensive for the majority of people demanding it?
[A]uthors in the digital age should design their books to be purchased or consumed in a more fine grained fashion.
Very true!
I've started, ever so slowly, to self-publish some technical books that I've deliberately try to keep small. I want to offer just the best parts, remove the fluff and filler: http://justthebestparts.com
It pained me to buy pricey books just for one or two chapters, and I see no reason now not to publish things in more digestible and accessible chunks.
In a past life I did some writing for Wrox Press (the previous, went bankrupt, version) and the editors were often very keen and having extraneous detail added rather than encourage people to either Google it or, perish the thought, go get another book (unless it was a Wrox book).