one thing that hasn't been mentioned is what happens in emergency situations when instinct kicks in.
i have had a couple of freak near misses, dogs suddenly in front of me with no warning, and in each instant i grabbed both brakes. and in both instances i know (well I strongly assume) i would have endoed without the back brake. i was very thankful for both brakes. most riders might have better instincts than me, but i feel the body memory of years of two brakes riding comes back to me despite four odd years of leg stopping. something happens in freak situations that takes us back to what our body kinda does on auto pilot...that's why i never feel quite right with just the front.