BOAC:
rrat "No one would design a system like you seem to suggest with" - your confidence is most impressive. Does it extend to knowing that no-one would design a system to shut off the stall warning in flight whilst the a/c is still stalled?
I think the problem here (system design wise) is what to do when the sensors are outside their reliable range.
Presumably the AoA sensors have some envelope in which they work. The system designers would not have turned them off for no reason. The most likely reason is that (for some reason) the AoA is not realiable at that airspeed. Or perhaps there is another failure mode they are worried about (don't throw stall warnings at the pilot if it could be because of a bad AoA sensor).
In this case, continuing the warning was the right thing to do (ie would have led to the least confusion). In other cases it might be wrong.
IMHO a better solution would be to put "?STALL?" on the display somewhere (ie tell the pilot "might be stalled but not sure"). It is hard to do when the normal stall warning is the verbal stall-stall though.