The documentation in wiki.maemo.org has always been public already in previous releases like Maemo 4.x (Diablo) etc. The Maemo 5 versions of that documentation are just an evolution of the Maemo 4.x documentation. In a way, you could think of that as "community documentation" or "SDK documentation".
Those of you who are already familiar with the Maemo 5 Human Interface Guidelines will notice there's overlap in the documentation between wiki.maemo.org and forum.nokia.com. That's quite expected as the each document has its own "roots".
There's ongoing work to make sure that there's no conflicts between the forum.nokia.com documentation and the wiki.maemo.org. Just remember that the forum.nokia.com is really a document archive in terms of Maemo 5 documentation. All the "live" updating work and collaboration continues to focus on wiki.maemo.org and other maemo.org sites.