I'm not a pilot, but I have a hard time understanding why the stall warning did not operate below 60 Kts, unless the engineers just didn't see the forest for the trees. The logic seems to be that since the AOA values aren't valid below 60 Kts, there's no way to know whether the airplane's stalled.
But if the airspeed is below 60 kts, how could the airplane not be stalled? I guess you don't want a stall warning sitting at the gate, though surely there are other ways to prevent that.