This is from the fact that (both of) the Mortal Kombat DVDs are in the "Warner Brothers cardboard snap-case release" line. I have found that the audio is inferior on nearly all of those releases, even including their box set versions of say.. Nightmare on Elm Street. Both the stereo and 5.1 tracks have both a clarity and level issue. It should be, by all accounts, a DVD surround and a BD surround of the same mix should sound the same, but they do not. And the stereo mix on a DVD should be better than that on a VHS, but it isn't. As such I have found that the VHS audio is better than the DVD audio on these releases.
It only seems to effect these Warner Brothers cardboard DVD releases. So because of this, the VHS equivalents are better because the sound is better. For any of the ones I've had like Mortal Kombat, MK: Annhiliation, Sphere, American History X, The Cell, Nightmare on Elm Street box set, etc.
Picture examples:
American History X:
http://www.ebay.com/itm/282410567889
Mortal Kombat:
http://www.ebay.com/itm/112376521989
Nightmare on Elm Street set:
http://www.ebay.com/itm/172630260190