One big reason robots aren't very good is because actuators are not very good. There are no good artificial muscles. Motors are great to power wheels and propellers but not much else. On the sensor side, robots can see, hear and even touch quite effectively. I think the software is slowly making progress, as is the # of computations we can do per watt. But lack of actuator progress severely hampers the future of robotics IMO.
Hydraulics and pneumatics work pretty good, but they are really tedious to work with, especially for people used to electronics. Their biggest problems are cost and seals, especially seal durability. And of course the cost in energy to keep them powered - when I get around to it, I expect to need to use a IC powered version out in the garage. But then energy budget is a problem with all mobile robots.
