Wow. I buy a couple of packs of Walmart socks (probably about $20 as you said) and that lasts me about the 8 years even if I'm using them for running and such. I wonder if there is some other factor (shoe fit, toe nails, etc.) that is adding additional wear?

On their website, for the warranty it wasn't clear to me if they provide the packaging and postage to ship to them, only that they ship for free to you. In that case, that might add to your cost especially if you have to do it multiple times (plus the hassle of actually shipping). I guess it really comes down to whether these socks are so good that you virtually never need to replace them vs if you're going to have to keep using the warranty every few years.