[Ramius]

Why robots when real mules are much cheaper, and hardier?

Well, for starters, a mule doesn't learn the way to where you are, and you can't send it back for more supplies by itself, or send it to some designated place on it's own.

[budwiesest]

and you can't send it back for more supplies by itself

Yes, for that, you need a Collie named 'Lassie'. ;^)