I don't know if this was always the case, but this weekend I just noticed that the wheels of the AI cars are not spinning when I see the cars in my rear view mirror.
Haven't noticed, but then how often do you see a car from the side in your mirrors? What detail level have you got mirrors set at? I have mine at Medium and they don't show car shadows. Maybe it affects wheels too, though personally I'm not going to bother checking.
The cars don't have to be side on to notice this. I have mirror detail on high. I'll check shadows next time I put it on. I may take a short video.