Pity you aren't near me there's a great place that does disc skimming if they aren't to far gone
Quite normal for my other car that has single floating caliper for the inside to rust but it shouldn't be an issue on 4 pot calipers unless there is an under lying issue with the calipers maybe the pads are binding in the carrier?
Binding pads on a 2008 calliper should not be an issue unless pads have been changed from original, whip them out and check.
