Situation: a reasonably nice young man who'd recently (within last 2 months) purchased a bike from our shop came in, and the rear derailleur had grenaded. I didn't have a chance to dig into it, but from what I could see, the spring in the P-knuckle, responsible for applying the pressure that keeps the derailleur cage pushing toward the back of the bike and tensioning the chain, had broken. The derailleur hanger was still straight to the eye, and the derailleur itself looked "normal" for a couple months riding - a few dings and dents here and there. Of course, he was JRA.
Now, I'm not unreasonable, but I'm also a hardened skeptic when it comes to the W-word. Fact is, there aren't that many defective products out there. Materials and manufacturing processes are great and getting better, and QC (most of the time) has followed the same trend. I know it happens, but if we accept Occam's Razor, it's more likely that a stick or rock got flung into the drivetrain, unbeknownst to the rider, rather than believing it was bad materials or manufacturing. Again, either is possible, but one is more probable.
Here's the rub: if this bike had been six months old instead of six weeks, the guy would probably have been singing a different tune. I am now going to coin another ABW truism: the purchase of a new product does not put into effect a moratorium on bad luck. Just because you put in a new tube does not guarantee you will be flat-free for any minimum amount of time. A new derailleur does not keep sticks and rocks out of your drivetrain. A new bike does not keep you from crashing out in the first turn of your Cat-5 shit show. I'm sorry, because sometimes that sucks, but it's not SRAM's fault, or Shimano's, or Cervelo's. It's nobody's fault. Sometimes, bad luck and shitty things happen, even to good, responsible riders.
I don't know what we'll do for this guy; it's not my call to make. If it were, I'd ask SRAM if they had any insight. They know their derailleurs better than I do. If they say the W-word, great. If they don't though, I'd have a nice heart-to-heart with this guy, explain the ABW Bad Luck Truism, and offer to comp labor on a new derailleur. If that wasn't good enough, I might go so far as to offer a discount on the new one, because I'm all kind and understanding and shit.