wallst, that is a good question. I never really looked very deep into how the compression works, but I've been told that it is close to perfect, with an occasional loss of a bit or two. Hence why I put the word "should". So uh....good question
Dolby does their compression one way and DTS does theres the other way. Regardless, the final product that you get out should be the same. The big difference in the two HD formats though is that Dolby TrueHD is a completely new format, and if you do not have a compatible decoder you cannot read it. So any TrueHD BD's are also required to come with a Dolby Digital 5.1 track. DTSMA is known as a core+extension, where if you do not have a receiver capable of DTSMA, if your receiver does DTS only, it can extract the data from the DTS core of the stream. Regardless, most BD's I've seen almost always come with a DD5.1 track, even if they have a DTSMA original track.
and tryton, does it say that it has a Dolby True HD track, or that it has a true HD track, meaning that it is labeling their sound as true high definition, and not as the name Dolby True HD compression?