I was calling you a troll Lew :p
I think what Bradock's saying is that when you bend the string - You're stretching it.
When you stretch the string, the stretching is distributed across the length of the string.
If the nut grips the string, then it won't stretch uniformally - Which'll have an effect, not neccesarily a negative effect I'd imagine, but hell, a nut is meant to be be perfectly transparent, and allow the motion of the string to be unhindered.
If the nut grips the string, then everytime you move the string through it (everytime you bend the string, stretching it and then unstretching it) it won't neccesarily return to its former position, and thus will reduce tuning stability.
Ofcouse, stretching and unstretching strings has its own tuning problems, but that's to do with the properties of the string, not the nut, and adding more complications again - doesn't help.