I think in order to have a book about music theory, there should be some explanation as to how to make music for some particular expressive purpose and not just the technical details of how to make sounds. A guide to constructing a piano is not music theory. I don't care if it's classical music or techno or gamelan, or if the theory is formal or traditional, if there's not some discussion of how and why to express musical ideas, it's a technical manual and has very little to do with music.