There has been talk about this and I've put some feelers out to my industry contacts but so far have heard nothing conclusive. HOWEVER, it's important to understand that the way that Dolby Digital, (core, plus, and True HD) are authored on BD and HD DVD is very different because of differences between how the two formats "packet" the data as well as differences between format requirements.
For instance, BD allows packet structures that permit standard (core) Dolby at rates up to the maximum consumer bit-rate of 640 kbps. HD DVD is restricted to the packet structure of DVD which caps Dolby Digital to 448. Dressler from Dolby has stated plainly at AVS that the 5.1 Dolby Digital Plus tracks on HD DVD are "equivilant" to the standard-Dolby tracks on BD that are running at 640. Bascially, Warner is using Dolby Plus as a work-around to increase the bit-rate to what you can get with standard Dolby on BD (6.1 Dolby does require Dolby Plus to encode the discrete rear channel, so this is talking about 5.1 mixes here).
There are also differences to how Dolby True HD is encoded on both formats.
On HD DVD, there is no provision for a "core" Dolby track in a Dolby True HD stream (which is basically MLP). So the bit-rate required for True HD is probably lower since no core is required. The downside to this is that no HD DVD player can extract the core 640 Dolby stream for those without LPCM capability over HDMI (or who have multi-channel analog).
The BD format requires that a 640 kbps "core" Dolby track be embedded with a Dolby True HD track for backwards compatibility with legacy gear. That would increase the bit-rate required for the overall track and may be why we're not seeing Warner duplicate True HD tracks on single-layer BD discs if their HD DVD file size was already maxing out the 25 gig limit.
That's just conjecture (my guess why the True HD tracks were dropped for the BD). But if it's somewhat accurate, as dual-layer BD replication gets better and cheaper the issue would be moot once the industry shifts to dual-layer BD as the defacto norm.
Yes. David's posts are very helpful with what is for me the most confusing part of the new formats, the audio. I've just got to start wrapping my brain around this stuff.
You likely mean IF the industry shifts to dual-layer BD as the defacto norm. Because right now, it's a coin-toss - especially with dual format players and discs likely coming to market.
As far as BD goes, dual-layer will become the defacto norm. That's been the goal of manufacturing/replication all along, just like with dual-layer DVD.