how is it different from say, a book?
Why do you think a recorded performance of a work should be protectable under copyright? It's NOT an original work of the intellect. It's a performance of what is often someone else's work. Just because it is recorded, should it be protected? Does the technological innovation of recording make it protect-able? And, if so, shouldn't the technological innovation of infinite copies at zero marginal cost make performances un-protectable?
I don't see any difference in a book and an original music recording in terms of why one should be subject to copyright and one not.
Whether recordings or books are protectable in practice is another matter, as it is very easy to make digital copies of both.
But if one takes the stand that an author of a book (be it an e-book or a printed one) has the right to set a price for a copy for her work, and benefit from protection by copyright if she so chooses to, I don't see how a recording of an original piece of music is any different.
But a quality reference book doesn't really have an analogue in music. That book can be a key tool to someone performing their profession. This applies even in a digital medium.
Whether the book or recording is digital or not doesn't really matter