having had a client who is a sound mixing studio, i know they don't take the sound used in film directly to dvd. they will remix the sound because theater sound systems are different from home systems, obviously. While they don't necessarily take different tracks from the film, sound volume of certain scenes may turn out different, because of the remixing. This may be the case. I don't know if it's obvious to everyone or not, but films get remixed for the various places they get played in, ie. dvd, tapes, cable, air planes and theaters. The film get remixed for each of those outlets. Sometimes, they're not even done by the same studios. For example, my client did the air plane version of Charlie's Angels, but didn't get to do the dvd version.