When you are searching books, the context often changes drastically, and you may want to search for two concepts being discussed in the same vicinity. For example, I am looking for information on GBS relating to "the divine right of queens." It won't necessarily be phrased like that, though. What I really want is a list of all pages that mention divine-right and queens, but what I actually get is a list of all books that have those words anywhere in their text.

Proximity search is not a necessary feature for web search, because websites are small. They also tend to be chunked up by concepts, with one large concept per page. But books are divided up by parts, chapters, or topic headings. If Google can't wrap their AI around those segregations, it would at least be nice to ask them to find your query where it occurs within a specific range of pages. This is similar to map applications that will find businesses for you within a specific radius.

I think GBS actually consider a range of two pages: e.g. if there is "divine rights" on page 54 and "queens" on page 55, it shows both pages.

But your point is absolutely right: GBS should search inside chapters, or inside a user-given range of page.

Though, I don't completely agree about the non-necessity of site-search (opposed to page-search) in the web search. My first post here was about this: http://blogoscoped.com/forum/30087.html

Open Source Shakespeare has a search interface that would simply rock on Google Books.

http://www.opensourceshakespeare.com/search/search-advanced.php