Striations are microscale. Microscale features are all that frozen rocks can do. Even there it is moving till, not moving ice, that makes the microfeatures... and the till is saturated. Dry till won't abrade worth shit.
See at the bottom of a continental glacier the pressure is enough to plasticize both the rocks in the ice and the rock the ice is resting on. Can you wear through a brick of butter by rubbing it with margarine? Hell no. But run some water across it and it will melt. Same deal.
How come you don't see any plucking or quarrying, say, in the Bypass Glacier cirque on Slesse? Cause there is not enough water. The ice is just a reservoir for the erosive water.