I just had my front pads and rotors changed. They were getting REALLY bad. And, like you, I was told I needed a new caliper because it wouldn't retract. It seemed weird to me, but the tech doing the job was a good freind of mine. I took his word and ordered a caliper. When it was installed I got a chance to see the old one...busted seals. Probably could have been rebuilt with a kit, but the whole thing was very rusty and crappy looking and a Suby reman caliper isn't that expensive.....well, for me anyway
So, the moral of the story is you can have a bad caliper and not really notice it if your brakes are horrible in the first place.
Dave (new brakes, yeah!)