It's only because there are a lot of pedestrians in urban areas, not because urban areas are more dangerous for pedestrians (in fact they are probably less dangerous).
Without some way to control for density of cars/pedestrians, this chart is quite useless.
A car can kill a pedestrian/bicyclist/motorcyclist at surprisingly low speeds. It's almost impossible to kill someone in a car at under 25 MPH or so (unless they drive off a cliff or something), but pedestrians can be killed by cars going as slowly as 10 MPH (they get knocked off their feet and hit their heads, usually). I read a very interesting paper by the NTSB or IIHS about that, but can't find it now.
Pedestrian and bicycle fatalities outnumber car occupant fatalities in Manhattan for this reason.
I saw a billboard last time I drove through NYC, explaining why the speed limit is 35 rather than 45. It basically said that if a car hits a pedestrian going 35, the pedestrian will probably live, but if a car hits a pedestrian going 45, the pedestrian will probably die.
