First of all, the possibility of ice is obvious. No warning is needed. That is just silly.
Second of all, it wasn't just a light. It was a loud noise.
Third of all, the warning was delayed. It wouldn't occur right when starting the car. It often jolted me for attention right as I was pulling out into very busy traffic. The warning was a hazardous distraction.
Partly correct. Yes, the possibility may be in part obvious by conditions such as temperature. But I think most people who are used to driving on icy conditions can tell you that the ice may still come as a surprise. A system that could _reliably_ warn about slippery conditions would be good.
Somewhere where it snows once every 3 years it might be helpful. When you live in a place with real winter it actually makes you less safe since your brain has to spend time processing the alert for a condition that's obvious since the entire horizon is covered in a blanket of snow.