'Which of these are not supported by CalDav/CardDav/GroupDav?'
You missed the point. Standards are useless if you don't have software that put them all together, and integrates the different needs.
If I setup a meeting, I need confirmation request to be sent automatically and responses processed qs well. And I like my mobile sync with all of it. While being able to share documents in the meeting setup.
Preferably, without a web interface only which is a pain to use on mobes/tablets, and often on desktop as well.
Kolab has still a lot to do to match Exchange. Our collaboration infrastructure is part of the money making, and, really, doesn't require much specific management being integrated with AD.
Biting the hand that feeds IT
