I've never understood this. Why not put a real edge on a powder ski? It's not going to hurt on soft snow, and if you hit ice on the way back to the lift you will have something to work with.
I actually agree with you. I was only restating the commonly held belief. My own skis are all either 1/3 or 1/2. The surprising part was that Fischer puts a 1/3 on that kind of a ski. Quite out of the norm...