Hi Uplinker.
I agree the stall warning should be "shaker". When the flight deck of AF447 was swamped with visible warnings and a continuous audible "C Chord" altitude deviation warning, I guess their brains filtered out the "C Chord" whist they turned their attention to the other visible messages. When the "Stall Stall" warning replaced the "C Chord" (higher priority) neither crew member commented (they probably didn't notice - like a ticking grandfather clock).
If you examine the flight deck transcript in the 2nd interim report, the "C Chord" was never canceled. It was only interrupted by "Stall Stall" and GPWS "Pull UP".
This U tube video shows how the brain can filter out repetitive audio warnings.
https://www.youtube.com/watch?v=YffmapFxt0M