Of course you are right about the 35mm being in HD it was the preview discs sent out to reviewers which must have had the 35mm audio not in HD.
Well at least it made it into the general release as i am sure fans would have wanted a disc swap program without it.
The excuses for the lack of the 70mm don't hold up however as they don't need to recreate that mix so much as track down someone who has a 70mm mag print that is not warped and destroyed. But Warners being a billion dollar studio certainly could afford it.
Its like the excuse of the 70mm mix of star wars no longer existing and we all know that fans have prints that have held up audiowise if not picture wise.
Yes despite being almost identical with the 35mm stereo just like star wars there is extra bass and oomph found in the 70mm not found in any other version.
Well until some enterprising rich fan has access to a non warped mag print and a way to get the audio off of it, we won't have those audio tracks.