I'm not sure there's a distinction to be made. An engine failure is a dramatic distraction, but if one doesn't understand angle of attack, any distraction will do. I suspect those other inadvertent stalls are precipitated by some lesser distraction.
An unintentional stall says more about pilot training and/or testing than about aircraft design. Anyway, there's a more direct method to evaluate a design: have it test-flown by someone with experience in a variety of aircraft and ask whether it did anything weird.
Different types of planes appeal to different types of pilots, which could account for some variation in frequency of stall accidents. I don't think it's fair to blame the designer for the faults of the pilots who like it.