Music in Japan tends to be highly categorized. Ongaku is the Japanese generic term for music, but most Japanese understand it to refer to Western music (the word yogaku is more specific). Hogaku (Japanese music) indicates both Japanese music in general or, more specifically, the music of the Edo Period. These terms contribute to the tendency to categorize, and musical audiences in Japan usually follow a strict division of taste according to category: Western, classical, hogaku, jazz, rock, popular music, etc.
Many Japanese who say they listen to ongaku really mean they care only about yogaku. I've met many people who are deeply informed about Western classical music but have absolutely no interest in Japanese classical music. They may be quite knowledgeable about 18th-century Italian opera but know nothing about 18th-century kabuki. The dividing lines are drawn quite distinctly in musical tastes.
This overspecialization of tastes is unfortunate. Even though musical form, structure and content may be entirely different, the joy of listening, for example, to a Stravinsky piece can also be experienced at a gagaku concert, or the rich tones of early-music instruments can also be found in the timbres of the shakuhachi, shamisen or koto. It takes, above all, an open mind and willingness to look through the form into the essence of the music. With a little imagination, openness and sense of experimentation, even a rock music fan can find something to appreciate in hogaku.