There are of course biped robots that walk. The Honda Asimo is the best known. But the Asimo doesn't balance dynamically. Its walk is preprogrammed; if you had it walk twice across the same space, it would put its feet down in exactly the same place the second time. And of course the floor has to be hard and flat.
Dynamically balancing — the way we walk — is much harder. It looks fairly smooth when we do it, but it's really a controlled fall. At any given moment you have to think (or at least, your body does) about which direction you're falling, and put your foot down in exactly the right place to push you in the direction you want to go. Practice makes it seem easy to us, but it's a very hard problem to solve. Something as tall as a human becomes irretrievably off balance very rapidly. When a robot is falling, meaning its center of gravity is not centered over the foot (or feet) on the ground, the error grows by e^(t/.5). If a robot gets more than a few centimeters off balance, it's unlikely to recover, because you just can't move the limbs fast enough to compensate.
Now, a week later, Dexter is so good at walking that the limit on the length of his walks is the size of room he lives in. Next step: a cage that can operate outdoors, so Trevor can take Dexter for a walk in the park.
The fact that it's 2k7 and the only real robots most people have ever seen are a Roomba and car factory robots on commercials is extremely sad. THE BOOMERS AREN'T GOING TO INVENT THEMSELVES, PEOPLE!
I believe it was Townsend Whelen who wrote that "Only accurate rifles are interesting." I think it's time to update that saying for the 21st century: "The only interesting robots are bio-mimetic ones."