I would imagine that the deleted scenes at best only have a 2.0 channel stereo mix at best. I doubt the studio would want to spend a lot of time finishing mixing 5.1 audio for scenes that were cut or incomplete. That would drive their cost up… This is because audio mixing usually one of the last steps in post for a AFX perspective.
You’re right. Stereo 320 kbps AC3. What a shame. We seem to have gotten the short end of the stick, and had our hopes up for something great. Seems Lucasfilm under Disney may be just as bad.