Interesting. There were a couple editing changes to the remaster at Cameron's behest (continuity error corrections, I believe) so the sound mix could have been conceivably slightly altered or revised as well, just to correct sync errors. Or maybe it was revised in the past and that's the master they grabbed for the DVD.

I know the MGM mono is not "fake", because that was the way I always watched the movie on that DVD, and all the familiar sounds are there. When I first bought the disc in 2001, I tried to watch it in 5.1, and couldn't get through the future war prologue before thinking "the lasers are wrong, the arpeggio is missing from the music cue", switched to the mono and everything seemed to be as I remembered it.