Rotors are cast iron. They'll rust unless coated. Areas that use a lot of salt in the winter accelerate the rusting. Surface rust on the friction faces isn't a problem. It'll rub off immediately. The problem is heavy rust inside the cooling passages that blocks the air flow. Here's what Raybestos says: Raybestos RPT Rust Prevention Technology* coated rotors use a propriety finishing technology to coat each rotor*s entire surface, including the cooling vanes. The full Grey Fusion 4.0* coating helps resist corrosion and significantly delays rust-induced performance issues. Note where they say, "...delays rust...."
The pads sound good. Less dust, long life, and great stopping power are always great.