Are you sure, because all the Japanese UE I have and those my friends have are only halfrate? And this review from Dvdtherapy says that the Japanese edition only has a halfrate track, and I´m pretty sure that´s correct.
I own the R2 Japanese UE version, because I didn't want to have to worry about the PAL speed-up issue, but I couldn't say if the dts track is full-bitrate or not, it sure sounds alot better than the R1 version though!