Multi User Blogs

Most of the technical blogs I read are individual blogs (like this one). Yet, most of the political blogs I read are multi-user. Typically, there is a primary poster – such as Josh Marshal from Talking Points Memo. But TPM has at least four other bloggers on their home page (Paul Kiel, David Kurtz, Greg Sargent, Justin Rood). I wonder why these two blogging communities are so different?