Reinventing the robotic wheel

So it looks like DARPA, the lovely armed forces research initiative, has been funding research for a "Legged Squad Support System." Basically they want a mechanical beast of burden that will carry 400 pounds of stuff and follow behind a soldier for 20 miles. This is going to require years of research and funding.

I guess I just don't really understand where the huge benefits are, with the possible exception of being able to tell an army of robot donkeys to deliver goods across the desert. Basically we're just using technology to create a far less efficient version of a donkey that runs on gas. I don't want to criticize the hand the feeds research, but I'm having trouble getting it.