But why not use a classic (model-maker's) Servo (or the "continuous rotation" type) ?
Because of the shape and size of a standard servo. The space they need to go is very limited.
Four of these small motors would lie in the palm of shadow bot's mechanical hand.
The driveshafts would face the fingers, and be connected to threaded rods. Nuts on the threaded rods would connect to the cords that pull the fingers closed. All the electronics would fit inside the wrist area.
The feedback pots are slider type and would also be connected to the nuts on the shaft.
The stepper Motors in the first post are connected to a really nice assembly already constructed and have a place to bolt them down.
We might even attempt to remove a stepper motor and connect a DC motor in its place.
From what we read about stepper Motors they are low torque low amps and not really constructed to handle this kind of a load.