[Suicide Junkie]

Calling it human-centric is irrelevant.

You could look at squirrels, who like to stand on two feet, hold a nut with two arms and chatter away with their sensory-and-processing organ laden head.

Heads:
- The speed of chemical signals is actually pretty slow. Keeping the brain close to the main sensors means faster reactions. This is also why reflexes don't go all the way to the brain, but just to the spine. You gotta get that hand out of the fire NOW, or you don't get to reproduce later.
For the brain to be near to more things, you have to concentrate those things in all the same place, thus forming a head.

- Appendages: Four is nice, but two are all you really need to get around, and using the other two for manipulators allows a lot more flexibility...
Raccoons, squirrels, and dogs use their front paws to manipulate stuff when they're not using them to run.
And those water-running lizards are pretty cool on two legs too.
Two manipulators are far better than just one, of course. Three dosen't add much more aside from juggling ability.