Cait Sith is a machine with a human controlling him. Much like Darth Vader is much machine with a human control (Anakin). Another thing is that they are both on the enemies side and betray their loyalty.
The black and white materia is the light and dark side of the force. They go to battle and the good side wins.
Darth Sidious and Sephiroths last moments were a lot a like as they both fell down a huge hole.
