Shipping logistics is a real issue. However the physical ultimate edition also launches earlier, It's not just the digital edition.
And why not release the other digital versions earlier as well?
There are so many holes in this theory for this practice that it doesn't hold up. Early access solely for the ultimate edition is nothing more than a way for MS to push people towards that edition.
Ofcourse it's it's designed to further incentivize the Ultimate Edition. There was a time when the UE didn't include early access... They took an logistical convienience and used it to sweaten the pot on a preexisting offer. I don't see why it's a problem. There is a difference between rewarding customers who invest the most, and inconviencing those who don't. People who buy the standard version aren't getting anything less or later than they normally would.
Why not give all Digital owners the game ahead of the street date? If I had to guess retailers aren't to fond of the existance of the UE. They'd likely be less excited if their physical versions were further disadvantaged in the competition against Digital. If you owned a game store how happy would you be to find yourself pushing and helping advertise a game, only to have even more of your customers choose to go digital because for the same price they can play it earlier? Publishers are surely interested in preserving their retail presence at this point.