minerals in the snow / wind blown grit / rocks / banging around in the ski rack, the lift line, hitting poles, etc.

You're right. Snow isn't hard enough, but, it's probably a mistake to assume it's just snow.

I think at a microscopic level, the sharp knife edge on your ski will become rounded after a few runs on ice just from the force involved. You are right, it has little to do with the nature of the snow crystals.