While I agree that there isn't much benefit to a 0w over a 5w unless you're in the arctic cold there are some reasons to run a 0w oil instead of a 5w.
Many american synthetics use lower cost Group III base stock in their "synthetic" formulations. You will find this in many 5w-20, 5w-30, etc products. Many 0w formulations use higher quality (and higher cost) base stocks in order to achieve the low viscosity pour points. Usually (meaning not always) better base stock = better protecting and performing oil (there is more to an oil than just it's base). This is just one example of why maybe you would want a 0w over a 5w (you did ask for a reason
I highly doubt Chrysler is going to run an oil analysis and determine that the 0w oil you put in your engine was the cause of a failure (if they suspected oil as the cause at all). I'd be surprised if they could conclude from an oil analysis that you started with a 0w instead of 5w.
At this point I will again suggest bobistheoilguy.com for research and discussion about oil. There you can find a specific oil that meets not only Chrysler's minimum requirements to make your engine last through their warranty period, but the requirements that you may have for your engine as well.
Not all oil is created equal although most oil will be good enough to protect your engine for a very long life.