You could buy a shirt and it came with the membership, or pay less for just the RSS membership. He delivered a personal RSS link with a random string. That worked until people moved to Bloglines, because it shared URLs among all its users and thus exposed private URLs to anyone looking for the daringfireball.com feed. At that point, he moved to password protected feeds, until people moved to Google News, which didn't support password protected feeds. This is when he began the weekly sponsorship model.