Disklavier

Hi,

I am playing a Pianosoft title and when using the digital reproduction 
of sound, the keys on the piano will move and digital piano sounds are 
heard.  Is the sound actually generated by the keys hitting the 
dampened strings, or is it totally relying on the MIDI information to 
generate the tone?  If I play the same song in digital and turn off the 
keys so they don't move, it sounds exactly the same.  I would assume if 
the piano is really playing (that is, not just reading the midi and 
creating the sound in the hardware) it would sound at least a little 
bit different, wouldn't it?

When playing as a digital piano, is the key movement just for show?