Like George Lucas, you've missed what makes any character recognizably human: behaviour and interaction. Puppeteers understand this. Sure, the appearance of an inanimate object evokes a first impression, but a bond emerges according to behaviour. In the case of the quadruped, observing its gait causes us to attribute cow- or dog-like qualities to it. In the case of artoo, it's his anthropomorphic courage and stubbornness, which we discover as for a ventriloquist's dummy, through his operator C3P0. In the case of the bomb disposal robot, similar courage is attributed because it does things the grunt would not.