I am interested as to what is different about this site compared to any other forum? How can I explain it to new users.
A forum is used to have discussions where you can have arguments against and in favor of a proposition.
Ask Ubuntu allows for a questions and several answers to that question. But not us to discuss about the question and the answer. That is done by moderation by users with up and downvotes, close votes and comments to ask for clarifications. Any form of discussion will be deleted by moderators.
Ask Ubuntu is a lot of things but a forum it is not.
A forum is a place for open discussion that doesn't have to stick to the topic at hand.
A Q/A site like Ask Ubuntu is about Questions:Answers - and their support system. There's no room (except chat ;), for veering off into meaningless banter and straying from the topic.
As such, anyone coming to Ask Ubuntu with a question should find themselves an answer, and if not, be able to find that answer eventually. It should do away with the frustration of going to a forum about X, and instead finding 50 pages explaining the meaning of "3".