Is "Onko heillä kirjaa" wrong? If yes, why?
I think it might be a matter of emphasis. It is the book, not just a book, and the closer the noun is to the beginning of the sentence, the more emphasis it takes. But, I could be horribly, horribly wrong.
No, that's exactly how it is. :)
Maybe it has to do with objektiivi..objective..where the emphasis is about the book..