Jus' sec here. AF447 had plenty of stall warning. It only stopped after the crew held it into the deep stall. The crew didn't register the warning or believed it spurious.
On the 60 kt criteria, I find it hard to criticize that design decision. It would get increasingly difficult to get reliable meaningful data from the sensors at that point (i.e. IAS vs CAS spread). And who would have thought an airliner would actually manage to be flown to that point.
Something I have never understood wrt this - is it possible for the a330 to be in the air with an airspeed of 60 knots or even 70 knots and NOT be stalled? If not then why inhibit the warning? Worrying about sensor accuracy seems to be missing the bigger picture wrt the purpose of the warning!