Bit of a long shot but has anyone managed to get free replacement brake disks from the dealer under warranty ? i imagine they will say wear and tear but before i but new i though it might be worth a shot
I actually asked the dealer last week, I said I knew it was only aesthetics, but can this rust be prevented somehow. He said it can't, just as stevoxi said, since it's untreated steel, and that it's only on surface and doesn't affect anything but visual impression.
He said that if it was giving me such a headache I could get it taken down from the car, protected properly and then sprayed with some brake caliper paint, but if it was him he would't do it nor be concerned.