If, as has been suggested, I am able to throw more "significant" encounters in terms of in-combat resource expenditure(thus life/death) type of encounters then the average of PC's being killed or even a TPK rises significantly with each encounter(law of averges). The PC's will always be at more risk than a single monster encounter for dying, having more "significant" encounters, as defined above, raises this exponentially. And in fact can end up putting a longer halt on gameplay than a days' rest(no ressurection at lower levels).
B.) If I am throwing "insignificant" encounters at them, well first I can do the same in 3e by having monsters with way lower CR's than the characters. But then this leads to(as has been defined by Hong) numerous boring encounters. So what exactly has been accomplished by per-encounter abilities to solve the 9-9:15 problem? It seems like a smokescreen that confuses the issue but results in nothing.