The difference is likely the ability for the community to flag and moderate a comment rather than an entire wiki and repository. That said, the wiki workflow,

The difference is likely the ability for the community to flag and moderate a comment rather than an entire wiki and repository. That said, the wiki workflow, permissions, and limitations in formatting may push people who are after a more durable store of information to create a GitHub pages site which is then managed with the same workflow (forks, pull requests, and reviews) as code, along with the ability for search engines to index the GitHub pages site.