I am very sure, Sony is not the only one who is doing ENCODING for BD, and it's funny to read about SONY and BDA encoding and replications from hd-dvd/vc-1/microsoft insider :)
as far as I know they want slowly go from PCM to DolbyTrueHD tracks... so it's maybe some transition ......... and I think Dolby TrueHD will be 20bit/48kHz and PCM will be 16bit/48kHz Marek