It would seem that the difference between a/c requiring flap extension in case of stall and those that do not is that those that seem to require flaps come with slats installed. To me this would make sense, as slat extension provides the upper boundary layer with more energy and might help reattach the flow. The types I know (DH8 and F70) are not equipped with slats and do not require flap extension for stall recovery. Tu.114