Alas, it's not the road FFG seems to travel as it is intended to gear combat towards certain gaming aspects. Makes sense if you're aiming at supporting game sessions less than 5 hours, which in turn probably makes economic sense. For the hardcore gamers this tends to be rather kinda meh though.
Alex
Surely it is the other way around - increasing the deadliness of combat and chance of "insta-death" is going to decrease the length of sessions. When PCs die, we tend to have to stop the game, re-jig the adventure to make it still work, take long breaks or end the session for people to make up new characters and backstories... Your answers to your own questions such as chance of insta-death on an "above average roll" indicate a game with a high turnover. If I make three rolls, then statistically, one of them is likely to be above average.
I think that's a common theme with advocates of 'an above average roll' leads to serious effects. People need to keep in mind that even small chances become near certainties after a few iterations. If there's a 20% of someone dying from something, then the average number of times they can face that situation is three times (80% of it not happening, times 80% times 80% = 50% of it having happened after the third time).