IIRC, the problem with DVD calibrations such as the THX Optimode is the method involved.
The Optimode calibration video/audio is intended to go through the same processing as the movie itself. As a result the Optimode for a given DVD is so you can calibrate your home theater so it is accurate for that DVD only. It is not an absolute calibration for accuracy.
(At least this is what I remember reading way back when. I hope they've changed that.)