It has become something of a commonplace to say that, in the 21st century, “serious music” (a term that I use reluctantly) has entered a definite period of decline, if not its death throes. In truth, it has even become something of a commonplace to say that such a statement has, indeed, become a commonplace. Thus, when I read the title of a lecture by Tom Service, who writes on music for The Guardian and presents BBC Radio 3’s “Music Matters,” I thought that it surely must be more of …