Couldnt you just move a heavish mass left/right in the head cavity say, rather than moving the head on the neck length, to move the COG.??
I suppose you could. I think the main criteria for designing a humanoid, walking robot are:
1) Does it walk like a human?
2) Is it a practical design? If not, defer to point 1) in redesign.
The problems with the head-weight are:
1) It doesn't move humanly. What would you use as the weight, by the way?
2) It's not practical. For the same amount of COG offset, you'd have to move a small weight in the head a great distance to achieve the same effect as moving a large mass (like the entire upper body) a very small distance. I leave it up to you to decide which moves more humanly.
I think a big difference between balancing buildings and balancing people walking is that one is meant to be balanced and stay still, and the other is meant to be balanced while in motion.
Wow! After only an hour on Youtube, my video already has two honours!