The only reason I bought AppleCare is because it covers battery degradation below 80% with no deductible. A credit card extended warranty is not likely to cover that, or if it does, I'd have to spend more than $29 worth of my time in dealing with them.
Also, being a first generation product, I expect these will have some more hiccups than usual - in fact I've just replaced two replacement buds today for the rattling issue that's somewhat common. Normally I don't bother with AppleCare on my iPhones or tablets.