If you don't allow for private discussion and post-mortems within a group of people, then the likelyhood of effective management and feedback decreases. This is not because the Wikimania team is being secretive, but because talking only amongst yourselves that know each other best gives a place to air honest feedback in a way that would not happen if that feeback between the team was forced to be public. Furthermore, there is sensitive information about things like sponsors, finances, relationships between people that simply don't need to be made public as it would cause more harm than good. Every chapter has a private executive channel, and even the Wikimedia movement has an internal mailing list - none of these imply that the rest of the community is "external" but simply that some things are best kept private. Furthermore, you can't actually force people to talk in public, all you do is drive it underground turning what is a legitimate internal discusison into a cabal.
wittylama.com/blogPeace, love & metadata