Scott, I know where you are coming from, I really do. It is incredibly frustrating when someone attacks you on a personal level of any type. However, I have talked to Zart previously, and he explained the reason there is not a zero tolerance policy for this type of language is that it can be abused easily. Now, I would side with you in a second if this was a continuous bombardment on you. However it was one negative thing. And really, I know I have been hit with worse things than that, and I'm sure other mods/admins have too.
Another topic is how you responded to it. Not only did you ban him but you put in a "comparable message". By the way, you took it an extra step. You are someone who writes a ton of guides. One of which is a guide on being a moderator. An exerpt from the guide:
You're expected to have a cool headed and social attitude towards the greatest jerks on earth.
You did not have a cool head. You let him get to you and you turned it right back on him. I understand he was an asshole in saying that, but there were many ways you could have handled that, and this was embarrasing. Practice what you preach.
+support for unban when template is used.