I'm pretty sure Darth freakin Vader would have his fake limbs made out of strong material, so one blaster bolt to his palm won't do much.
But yeah, the Jedi uses the Force to foresee where the bolt is going to be and they place their lightsaber accordingly.
But even a Jedi can't move his Saber to deflect like 30 bolts at once, i.e. Geonosis.