Although the show had a specific singer in mind, his point was that all of the musicians/singers/composers who existed before recording technology left no mark on history.
OK, it's true that, say, Beethoven left his scores, but in some ways you can't be sure that the material is being played in the manner intended by the composer unless you hear it firsthand. And famed singers of the Nineteenth Century or before left nothing; they were ephemeral. Nowadays even minor talents leave trails of their music that almost anyone could follow. Is this true immortality?