It depends on the book with learning, for example if I pick up a historical novel set in a period that I know little about or a mystery set around something I don't know, I would feel disappointed if I didn't feel like I had learnt quite a bit from it. But in general, I agree. :)

Although, I also recall a book that really annoyed me, because it was a mystery that left a clue out commenting that it was too obvious to state, which I didn't manage to work out until after the end of the book.