Cost and reliability (Score 1)

You can't buy a car for $10,000 these days, I have a feeling autonomous machines that are significantly more complex than cars are going to cost a hell of a lot more than that for quite some time. Then there's the reliability factor. That $10,000 car is going to have all kinds of problems over its usable life, and we've actually had plenty of time to work out the kinks of building cars. It'll cost another fortune to maintain an autonomous robot, especially if they take the route of "upgrading" models every year. After all, if your cashier at McDonald's breaks down, you just find another minimum wage slave to replace them. If your robot cashier breaks down you're on the hook for hundreds of dollars an hour to fix, or tens of thousands of dollars to replace, it.