One of the reasons for a lack of TrueHD was that the HD DVD uses a version of TrueHD that BD doesn't support (BD uses the version with the 'core' legacy DD stream).
As for the lack of an equal-in-quality-but-resource-hogging 16/48 PCM track, I'm at a loss for explanations. With the space and bandwidth advantages of the BD50 there was absolutely nothing stopping them, as you said. Not only that, but PCM is actually cheaper to use because there are no royalties that need to be paid and there is no need for additional encoding. This happens to the BD version of every TrueHD-equipped HD DVD Warner puts out, and I don't know why.
Hopefully this lousy habit will come to a halt soon.