Why is Dolby True HD going the way of the Dodo?

[Jeff Kleist]

Gotcha! But if the studios were to eliminate the extras and lossy/foreign language mixes, will this result in better AQ and consequently PQ by maximizing bit rate

They're not going to get rid of either one. Given that most reference Blu-ray experiences come in somewhere in the 35GB size for the movies, it's maximizing the available bandwidth for scenes of high complexity that's more important than raw disc space.

Running high bitrate isn't necessary all the time, If you look at Star Trek TOS or the new Gone with the Wind, you'll see they get along with superb picture at well under 20mbps on average, because they're low complexity and fairly static productions (compared to today's movies). Throwing 15 or 30mbps at that isn't going to change much.

Dolby and DTS are catch-all codecs that work with the latest stuff and have the legacy built right in that will work on JoeSixpacks existing equipment, that's another reason why they choose them, because PCM comes out as stereo over optical.