They (readers of the book) should do the rating through iTunes and not via a cheesy link within a book back to iTunes. Such a link (if it even works) will close iBooks (or whichever reading app they are using) and open iTunes. That would definitely piss me off if I was reading such a book. I hate it that so many of the free versions of paid apps bug the crap out of you to buy the paid version. This would be just as annoying. A simple statement at the end of the book asking the reader to please rate the book in iTunes would be much more appropriate from this consumer's point of view.