Really? I mean if I'm willing to pay and they do replacements anyway why wouldn't they? Although I'm sure you know better than me, but can I ask why?
Just to give you an example why I doubt they will....
I was at an apple store yesterday to buy a case. I got one of the clear plastic ones that comes in 2 pieces that snaps together over the phone. I bought it, got out to the car, and wanted to see what it looked like actually on my phone. My phone had fingerprints and stuff on the screen and back. I didnt clean it up before I put it in the case, I just wanted to see what it looked like, take the case off, then put it back on once Id wiped it down really good at home.
I get the case on, then I cant get it off. I pryed and pulled and it just would not come off. So I go back in and talked to this sales girl. I said "I feel really stupid, I just bought this and I cant get it off." She said she had the exact same case and you just "have to pull on it with alot of force to get it off." She tried for a few minutes and couldnt get it. She handed it to me and said "I dont want to break it, you just have to really pull it apart."
Well I said "I dont want to break it either, dont you have a tool or something you could pry it apart with?" They have these special tools to open ipods or mac minis. She took it to the genius bar and asked the guy and I heard him say "absolutely not." So she hands it back to me and says "sorry, you'll just have to get a screwdriver or something."
So, Im guessing if they wont help me get a $30 case off my iphone, they wont be replacing the back casing of one.
But like I said, who knows?? Maybe they will for a price.