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.