DPL = Dolby Pro Logic (used with Dolby Surround soundtracks)
PCM = Pulse Code Modulation: the format used on CD and LaserDisc, and the occasional DVD.
Uncompressed linear PCM soundtracks on LaserDisc (and some DVDs) usually sound better than the Dolby Digital 2.0 (stereo) soundtracks commonly found on DVD. This is probably what the posts you have been reading are referring to.