Actually, the uneven brake wear on the "N" chassis cars (ie. the inner pad wearing out before the outer pad) is a normal condition. Now, if the pads are SEIZED into the bracket, that is usually caused by rust building up under the shim on the bracket side.
I have yet to see a seized caliper piston, but we usually don't see many very high mileage cars at the dealer.
There have been quite a few times where the calipers creak or squeak when appying the brake, but that has turned out to be the piston contacting a small area in the bore of the caliper, but not a siezed piston. This is/was a common condition with all "N" body cars. Malibu, Grand Am, Alero.