Incidentally, Napster is vicious parasitism off musician's creative work. There used to be fines against some of the napster users. I'm not sure what the system is now, but the napster system as it started should have been dealt with by the courts via fines against some of its users.
To the extent that Napster charges its customers to access other people's work, yes. But as a musician, myself, I think the development of digital music has invalidated the whole model of charging money for a recording, at least in its bare, digital form. An MP3 song is best seen as a free commercial for a band's live performance, or for a more elaborately packaged CD version of the recorded work that includes additional products and benefits for the customer. Customers who don't want the extras, or who don't like the band enough to pay to see them live, can just listen to the song...and maybe they will like it enough to virally market it to a friend who will pay for the content. Either way, considering the casual listener a thief is unnecessary - they aren't stealing anything significant from the artist.
Of course, the music industry - which relies heavily on artificial acts with little talent who can't deliver quality live performances without expensive lighting, lip syncing, and a hundred backup dancers - realizes the game is up, and are collectively lashing out at reality in a blind panic. :)
On a song and its worth, see “minstrel.”