Because higher bandwidth was one of BD big claims. You best believe BD made sure that this movie more then any other would be perfect. I knew for months this would be their pet project. Looks like they hit it out the park. I believe its better considering DD+ is the lowest HD audio versus BD with months to perfect a comeback using a high bandwidth codec. That being said we hear what we want to hear, what we expect to hear, making a need for a double blind test. Technologically on specs how could BD not win versus DD+ but then again the higher bandwidth spec didn’t pan out with PQ?
If the video codec was unchanged then an increase in bitrate would not deliver differant picture quality. I do not remember any complaints with the HDDVD version as to macro blocking or poor visual quaility. In fact if I remember correctly, there was not a lossless audio codec on the HDDVD so that the studio could provide the best picture possible. Given their direction then, why would there be any differance in video quality?
Now as for the audio, this has been hashed over here time and time again. Debate about wheather a true lossless audio codec would sound better then a lossey one. Technically speaking a true lossless audio codec done correctly with enough bitrate to support it should sound better then a lossey one on equipment that will support it.
Any signal that is bit for bit without need for compression and uncompression to calculate that bit for bit transfer is always going to be the better signal for reproduction of any type of signal, and that goes for video and audio. But as I said, this has already been debated till the shoes fell off.
If you have the equipment and can enjoy the DolbyTrueHD then do so. If you already have this on HDDVD then the questions begs -- why even worry if one outdoes the other -- just enjoy the version you have.