I can only speak of what I was told. Don't take away something from my comments that aren't there.
Of course that wouldn't be the only factor, but I was told it is a factor (it being the styles of the 4 backs.) AT and Newby have been running neck and neck for much of the camp. At the same time, Cross has stepped up (mainly his blocking) and has the coaches more confident than they were. Ameer will need a breather and lighter workload. Instead of having Cross and AT (similar styles) come in to provide that, the staff prefers to have Cross and Newby taking part of the load.
But yes, some also has to do with AT. He can greatly improve himself by adding leg strength. A RS year would be perfect for that (if he redshirts.)
I am NOT saying that AT is ahead of Newby and that he may be redshirted because of his style. I am saying that the two RBs have been neck and neck throughout the camp, and if they remain that way, and the staff wants to RS one of them, it makes more sense to redshirt AT.