Style is part of it...as you can see, the Guides still have the old style, and we haven't had a chance to look at how we can freshen that part of the site up.
The Guides are also running on outdated wiki software that we'd like to upgrade, but just upgrading that portion messes with some other things in the site's operation, so it's a bit more than just adding a tab at the top of the new main page.