Whereas everyone else provides both seat of pants + stick shaker.
The question of stall warning is interesting indeed. Remember that the Airbus AoA protection should prevent stall in Normal Law. The probability of being in Alternate or Direct Law AND the crew allowing the aircraft to get into the stall regime is minute, regardless of how often we discuss the tiny number of cases in which his has happened. Nonetheless, these accidents demand a response.
The question is then; in the cases under discussion, did the crew fail to recognise the stall condition, or recognise it but fail to react effectively? There is some evidence that at least one pilot in both the AF and Air Asia recognised a need to push forward on the stick.
Should Airbus provide tactile artificial stall warning in reversionary flight control laws? Historically, aircraft were designed to give natural stall warning through buffet. Where this was inadequate, or the consequences of a full stall were intolerable (deep stall, for example), artificial stall warning was added in the form of stick shakers or even AoA protection in the form of stick pushers. Another important certification requirement is that the pilot be able to clearly identify the stall itself. The following is the relevant part of CS25:
d) The aeroplane is considered stalled
when the behaviour of the aeroplane gives the
pilot a clear and distinctive indication of an
acceptable nature that the aeroplane is stalled.
(See AMC 25.201 (d).) Acceptable indications of
a stall, occurring either individually or in
combination, are –
(1) A nose-down pitch that cannot be
readily arrested;
(2) Buffeting, of a magnitude and
severity that is a strong and effective
deterrent to further speed reduction; or
(3) The pitch control reaches the aft
stop and no further increase in pitch attitude
occurs when the control is held full aft for a
short time before recovery is initiated.
If the above cannot be satisfied through the natural characteristics of the aeroplane, then the manufacturer must fit artificial devices. In the case of the Airbus types under discussion, deterrent buffet is always reached before the point of stall, and the stall itself is naturally benign. The deterrent buffet is of such a magnitude that I doubt a pilot would reliably feel a stick shaker. Aerodynamic buffet has always been the classic natural indication of stall, from the most basic light aircraft upwards. The Airbus doesn't have a stick shaker because it doesn't need one! Whether we as an industry are training pilots to correctly respond to a stall is another question...