All that being said, I don't know why studios don't just go LPCM everywhere? Why even bother with DTS-HD MA or TrueHD? Same end results and with the storage capacity of BD it's not like space is an issue...
Storage capacity is only part of the issue. The bigger factor is the maximum allowed bitrate of a BD is 36 megabit/sec. A 7.1, 48 kHz, 24-bit PCM track takes over 9 Mbps by itself. Adding multiple languages would quickly use up all the available bandwidth, leaving nothing for the video or subtitle tracks. Dolby's and DTS's lossless compression can easily achieve a 25% reduction, and routinely exceed 50%.
I don't think that would be an issue until ou get to >8 channel audio.
BD drives read at a 1x speed of 36 Mbps, but the BD spec allows for AV rates of up to 48 Mbps. Of that video can be a maximum of 40 Mbps. 8 channel LPCM audio at 16-bit/48khz only requires 6.144 Mbps. There's still the full 40 Mbps of available AV b/w for video.
Even at the 36 Mbps read rate it still leaves ~30 Mbps which is still more than enough to encode very high-quality HD level 1080 AVC or VC-1. In fact, The Dark Knight, with its outstanding video quality is encoded at an average rate of 24 Mbps. I haven't checked but I don't think it even peaks near 30 Mbps.
Also, multiple audio streams shouldn't affect this since you only play one stream at a time.
I agree that the lossless compression options give the disc producer a lot more headroom and freedom with the bandwidth, but from a practical perspective it doesn't seem to be a real problem today and an easy way to save on additional licensing fees during production.
A much better way to address this long term would be for players to read at greater than the 1x speed (36 mbps) so that they could fully utilize the full BD AV bandwidth of 48 mbps....
