Thanks for the comment. That was debated slightly, in a previous HN discussion, where some pointed out that using browser defaults appeals more (to some people, I don't know if the majority), especially if they have particular needs. I admit to insensitivity to such things, but I will make a note to try your suggestion sometime. :)
A little CSS (max-width: 700px; margin: 0 auto;) on the body would go very far.