Because every project needs to start and end somewhere. There are disabilities I’m not covering at all. There are certainly more than 25 things that *every* site should implement. And so forth. Focusing on weblogs lets me delve deeper into specifics about implementation. This is already apparent in day 6 -- talking about the specific templates in each weblogging system that you need to check -- and it will become even more important later on. Many of the standard arguments against accessibility (my client doesn’t want it, it’s too expensive, the site needs to look exactly like the brochure) don’t apply to weblogs, so I will use that to my advantage.
Concentrating on implementation sounds like a great idea—there are several accessibility resources explaining concepts but I haven’t seen any that explain how accessibility can be achieved, especially by web content creators who are not HTML experts.