I would guess that they are using it as an antioxidant at those lower levels rather than as a friction modifier as used in the higher moly formulations. As I understand it, large amounts are needed to act as a friction modifier due to surface competition with the esters. As I recall from extremely limited data, I got the impression that TAN buildup seemed higher on the high-moly formulas than the no-moly formulas. This makes sense as the amount of sulphur containing additives can influence acid buildup.
Interesting that they went from zero moly to 100ppm. I wonder if TBN is also impacted by the formula change.?