I've only ever seen any rust when it's been raining and the rust gets ground off, only a tiny bit even then, with some rust runs down the spokes I am, however, running stoptech/centric discs at the rear and how the compound works in tandem with the disc is also probably a factor.
Very strange though. Either way it's a pain the the arris staying on top of polished wheels, only made slightly easier by keeping a coat or two of wax/sealant on them, gtechnic wheel armour is excellent on the painted faces though.