Justin,
The reason rotors are CAD plated are multifold.
First them keep them rust free while in storage and so they look pretty when the customer buys them.
Second, they are *supposed* to prevent rust from non-swept surfaces (most importantly the inside vanes) so that air flow is not inhibited by rust buildup. Also, just as important, is so that the rotor had does not rust against the hub assembly (happened to my brother's legend rotors once)
However, most poeple just do it so that when you wash the car the edges of the rotor don't look like crap.