They sometimes have to change because the rights to the Original Soundtrack to the movie had no provision for release on DVD or the Artist wanted to uch for them to release it to DVD. One example of this was the TV show "Tour Of Duty" . They had originally used music by the original artist from the 60's and found out that getting them to release the rights for all seasons would cost to much so they re editied the music and used cover artist. The sales sucked worse then an Obama speech.
