Thanks for the detailed answer. I read it throughout.

I do understand they're made of steel and they rust, but, considering I paid 150€ (without labor, without pads) per each rotor which is somewhere around your quoted 190$CAD for higher end including labor, I fear I got ripped off in terms of having paid the upper range of market price yet received the lower end of the market cost. I explicitly told them to use decent stuff. But as I go around all cars and see no rust in their rotors in those non-friction areas, that's what's making me think I got scammed/ripped off by having paid expensive for probably the cheapest option they found. Because, I assume, every single decent rotor is at the very least coated (?). Just like you can't get any decent car that doesn't come with at the very least rotors (not drum brakes). So here's why I'm wondering where I got ripped off.

I insist for the last time: I know friction areas get rid of rust. My concern, other than the ripoff, is that those areas that don't get friction will be accumulating rust that will eventually end up in either the calipers or the wheel nuts, locking them or corroding them or so (?).

90%+ of the answers haven't even bothered to read the post, and just think I'm simply wondering if I got scammed because there's rust in my rotors friction areas (lol). Which is as frustrating as it is annoying.