Well, we've had two different sets of rules apparently for the B737NG, which are not entirely in agreement. The one VK quotes allows it. the one None quotes does not.
Personally, I would not fly on any aircraft with ice or frost on the upper surface, and if I saw it while seated as a pax would draw crew attention to it.
If they showed no signs of concern I would deplane myself, regardless of how upset the cabin crew or airline got. I have no desire to die as a pax when I know the aircraft is in a fundamentally unsafe condition. I regard my life as worth far more than the cost of a ticket on a different airline.