The problem is that differences in tire diameters are constant where turning has a duration of a few seconds. Some AWD units are quite sensitive to differences in tire diameter - some are not. This board has had many, many posts of failed AWD units because of differences in tire diameter - and many of those vehicles have notes in the owners manuals about the subject.
But some AWD units are pretty insensitive to tire diameter - but it is difficult for a tire shop to know which are which - and since they are usually held liable if an AWD unit fails after replacing a single or a pair of tires, they use universal rules that will prevent damage in ALL situations.