Earlier quoted context omitted.
> stopped in a place other drivers might not expect You should expect drivers to stop at intersections. You should normally leave enough space between you and the car in front to avoid rear-end collision, even if that car stops suddenly. And there's already a signal the car in front has slowed - their brake lights come on. (Maybe that's not a US thing though?)
Well, for one people do not expect drivers to stop at a green light, like was the case here. You might wish everybody was well aware of their environment, but the fact is, a green light is a strong signal that makes people assume the other drivers are moving or are going to. The second point is completely off-topic, as the car in question had plenty of space between them and the Google car's rear-end. It just failed…
Watch the video. The self-driving car braked because the two cars in front of it did.