Car accidents typically involve a car running into a robot, which might obliterate the robot but would seldom cause injuries to the driver. Delivery robots would almost exclusively operate on sidewalks of 25 mph, maybe 35mph roads. Running into someone is also unlikely to cause serious injury if the robot is kept to a reasonable size and weight limit. Obstacle avoidance and bump sensors are trivial to implement. Drones, on the other hand, can take out eyes and cause severe injury if they impact someone in the face with spinning blades, and crash avoidance mid-air involves an advanced control loop as opposed to just cutting power to motors.
Well, I agree. The idea of a UAV with a 2m wingspan landing somewhere near my house to deliver a 5kg package sounds like it could cause a lot of injuries. The delivery vehicle has to be much larger than the package and it has to land near a spot that is accessible to humans so they can pick the package up. As soon as you have flying drones they will have to get near other humans. Ground robots have a huge advantage in that they are less dangerous to humans. Do you really think something that is designed to constantly cooperate with humans is going to fare worse than something that will be near one for a minute? It's very likely that the UAV companies don't test their landing programs sufficiently.
