The subtitle is "Why people get Rothko but don't get Stockhausen".
So you'd expect that most of the book would be concerned with that question.
Of the seven chapters, the first explores the question interestingly. For example, people pay huge sums for paintings and sculptures, and millions of people have flocked to the Tate Modern art gallery, but these same people recoil in horror when they hear non-commercial music (whether you want to call it "art music" or "contemporary music" or "experimental music" or whatever).
The seventh chapter looks for an answer to the question. Ideas considered include: the cachet of owning a unique original; the consequent possibility of financial gain; the ease with which one can walk away from a painting after a few seconds; people's willingness to "put up with far more crap visually"; corporations' desire to sanitize their image by owning visual art; etc.
But the bulk of the book, the middle five chapters, are basically the author's views on various artists and (mostly pop) musicians of the last 50 years. He likes Sun Ra and Jimi Hendrix and post-punk, and dislikes the Beatles and Damien Hirst and Tracy Emin ... but what does this have to do with the book's title and subtitle? Nothing. The author is simply telling us what he likes and dislikes, and trying to pass it off as a history lesson.
Great title and subtitle. Shame about the contents.