Not necessarily. Think of FAQs for mailing lists as an example. A wiki for a blog, even a group blog, is a bit unusual (at least, I can't think of any), but I don't see why the principle couldn't work. Each LW post is a work by a single author, idiosyncratic and focused on a single aspect. It'd not be surprising if a comprehensive wiki article - which draws on and summarizes/synthesizes each relevant post - could be very useful.