See here: http://dvd.ign.com/articles/753/753006p2.html

Somebody want to explain this to me? How are they doing this?

2 seperate encodes of the main movie/video, filling up a DVD-9 and ruining PQ potential due to heavy compression for lack of space? The PiP commentary box "hard-subbed" into the second encode? Or what?

Will the upcoming BD release of this film on Jan. 9 have a PiP, video commentary feature? In light of this, it sure as hell would be funny if it did not...

The Descent BD has PiP. And regular standard, old fashioned DVDs such as The Goonies and Jerry Maguire have it too. Doing it isnt rocket science. Cost and time to implement it is the real issue.