A co-worker has a C6 'vette with those open-spoke wheels that are so popular now where you can see is acres of rotor between the spokes- his develop visible surface rust within an *hour* of him parking the car on a rainy day. But its still just a trace of rust by the end of the day-not big honkin' flakes like that.
I'd say you got some very low-quality (made in China?) rotors there, because I've NEVER seen that much on a daily-driven car. Not all cast iron is the same- the trace metals (nickel, zinc, chromium, etc) used in the alloy can make a huge difference in the hardness, heat resistance, and (yes) how fast the rust develops and how thick it gets. These "trick" cross-drilled aftermarket rotors tend to be some of the worst IMO.