"Exclusive" pretty much means exclusive. E.g. the publisher would not want to spend a lot of time and money into promoting a book, only to have the author have the same book available on his/her own website at a lower price with 100% of the profits.
A real world example of this is the US Chess Federation's rule book. The 5th edition was published in the early 90's, and a book was pretty much the only thing that made sense. After the web came about, a lot of people asked why the rules weren't available on-line, and the board members pointed to the agreement with the publisher that they had exclusive rights to publish the material. Of course with the latest edition of the book, they're still not publishing them on-line, so maybe there's more to the story.