It's much worse. A wiki still consists of pages of documents, even if they're kind of improvisational and perhaps incomplete. A chat log is just a log of people chatting, with all the free-wheeling and meandering conversational style that entails.

Forums fall apart when you're trying to do things like realtime debugging. With a chat client, I can leave a window open in a corner and keep an eye on it while doing other things. With a forum, that becomes a game of hitting refresh every thirty seconds waiting for new messages.