Quite possibly. Maybe the difference then is that holding a coffee mug isn't an activity in itself, but typically combined with other activities whereas driving

Quite possibly. Maybe the difference then is that holding a coffee mug isn't an activity in itself, but typically combined with other activities whereas driving shouldn't be combined with other activities. It's possible that a sustained "don't use the internet whilst drinking from a mug" campaign could reduce the droppings(!), but it seems like a different class of problem than driving whilst distracted.