DVD players are locked in firmware as an agreement with the MPAA (their idea to curbing piracy from different regions... most notably the Asian markets infiltrating the US) and DVD player manufacturers (and I'm sure the US government was involved there somewhere.)
On the PC side, there are a few software items that create a transparent layer between the DVD playing software and the DVD drive, thereby faking the DVD drive into thinking it's playing the correct region (and still, this only works for certain drives.) However, I don't know of anything on the Apple side of the fence and your only option becomes the DVD drive firmware flash which will void your warranty and could make your DVD drive completely inoperable.