Why not just parent objects? If you don't use any kind of change to mesh when moving or rotating parts, armature is not needed. Just parent the parts to each other. Then move topmost one in hierarchy, when you want whole robot to move. If you want, for example, rotate a leg for kick, rotate the leg and the foot moves with it...

Unless I didn't quite catch your meaning.

I just tried, what I said, in Blender 2.54 (SVN version, self compiled) and it work as I suppose it should...