rotor and surrounding area rust is environmental mostly- namely because the car manufacturers save money and don't paint or use rust-proof components. after u wash your car, u will notice that the rust is especially more prominent.
u can either drive around and brake hard to get rid of some it it, or opt to paint the rotor & chassis. painting is a pain in the butt tho, cuz u have to remove the wheels, calipers etc. and, u have to use paint that is formulated for it due to high temperature concerns.
on the rx-8 forum, a lotta guys have painted it themselves. and there are many threads with step-by-step instructions on how they did it w/ photos. a lot of them look absolutely fantastic after it's painted.
for me, i just live with it best i can. i usually wipe down the area as best i can after a car wash, because the rust comes off really easy when it's softened up with the water. then i drive around and brake hard a few times and then it dries.
in the end the pursuit of perfection is a bit of a losing game.