Part of my job involves handling my company website. Along with that, I am usually the first to see and hear from customers and I can say that a lot of that Surly post is right on the money. It's not what you should say to a customer, but it does deal with the feelings you may wish you could express to them. You'd be surprised (or maybe not) and the ridiculousness that people try to pass to you, or try to scam you with.
Reading the Surly customer service warning reminded me as nothing more than a joke. Some people may get it, some may not. For the person who stumbles across the internet to find that page somehow and decides to not be a customer, you'll just as easily find another who thought it was funny or just didn't take it seriously and will purchase their products anyways.