I think some people are missing the point when they say it's the spectator's fault, or questioning why the driver should stop, etc.
It's not a matter of whose fault it is. It's a matter of whether a person has a moral or ethical obligation to render assistance when another is injured as a consequence of what the first person was doing -- regardless of whose fault it is.
Consider this scenario: a group of construction workers are working on the side of a road; they have set up all reasonable precautions to make the worksite as safe as possible for passing traffic. A car ploughs into the worksite, smashes into a pole and the occupants are seriously hurt. Should the construction workers render aid to the occupants of the vehicle, even though they had taken all reasonable precautions for traffic safety? Imagine if you are a family member or loved one of the occupants of the vehicle. If you found out that the construction workers merely continued their work without attending to the plight of the injured, what would you think?
Speaking only for myself, I think it's a terrible demonstration of how selfish and heartless we have become as a society if we know that people in our immediate vicinity are serious hurt or in imminent danger of death, that we are able to provide some kind of assistance for them, yet choose to do nothing.