The point of reduced speed is not to avoid killing people when striking them, but to reduce the odds of a driver losing control of a car and ending up on the sidewalk.
Sure, a car going 5 mph is still going to kill you but is easier for the driver to control so it doesn't. But again, "reduce the odds." I don't care how slow you're forced to go around that curve, there's still nothing between you and me on the sidewalk but your hands and feet on the controls.
