I know Dario Argento's Suspiria and Opera Limited Editions both come with a seperate CD with the movie's score on it, which can be play on any CD player.
I don't know about should, but it's nice when they do. It may be a pain for some movies though if it doesn't have that great of a sound track, and making them only play on DVD-ROMs makes them less then half use useful to the buyer.
"You were great in your day, Superman. But when the time came to cash in your chips, it was only natural that this diseased maniac would be your banker." - Lex Luthor, Superman 1978
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