I've noticed the same issue.
emumovies for mame, play fine in sync.
emumovies other emulators (atari 2600) exibit this behavior.
using gspot:
Atari 2600
audio - 128kb vbr 44100
video - divx 5.0 br 145kb/s fps 30 320x240
type avi
mame
audio - 56kb cbr 22050
video - xvid br 1183kb/s fps 60 320x240
type openDML avi