Actually, you can write a hundred page book that is about someone elses thousand word article and include the entire text of the article as part of the book and that would be considered fair use.
Now, in the case of cached pages on search engines, this probably doesn't apply -- but it's important to a discussion of fair use to understand there are situations where an original work in it's entirety can be used by someone other than the owner.
Now is each page of a website it's own original work or is it like a page in a book -- only a part of the overall original work? I can think of sites which work one way and others which work the other way.
Amazon.com shows sample pages from books it sells without obtaining specific permission from the original author. Amazon must do it because it helps them sell books -- the authors (or publisher) must not complain because they consider the net effect of what Amazon does to be more beneficial than trying to stop Amazon.