I've both heard and read that cats survive falls from under a certain number of stories and over a certain number (I can't recall either one), but in between can get hurt or killed. The theory is that they can survive the impact of a pretty high fall, but if it's in a middling height they have enough time to tense up so they get hurt or killed more frequently. Lower falls they do OK with because they flip over and land on their feet usually.
Cat falls