Gwilo didn't mention anything about stopped at lights.
Again though, if you feel (not saying you do) that it 'can' be no real issue in certain cases if a person is on a mobile is stopped traffic, maybe write to your MP. It's currently illegal and not allowed. If any of the other distraction comparisons are not illegal, if you feel strongly about them too, again, maybe write to your MP.
Personally, I'd love it if they got every single person who uses a mobile, hand held, when in a car, off the road. But they 'only' get 6 points and a £200 if caught. I can't change that, but, you guessed it, I have written to my MP!