Morbo, very good question indeed. A forum as it has evolved is a descendant of the usenet. It is a public space for topic related discussions. Several primary concepts include:
* threads, with messages by users
* threads structured into a tree (develop, projects, meta, ...)
* all messages are public by URL
* it is administrated by the owner
This forum contains discussions which can be found nowhere else. People can read up the discussion. It is "centralized" by design and that is important. If you think about it Bitcoin is highly centralized in one regard. The blockchain is a public data source. So the words central and decentral are much too crude for good analysis. With current known techniques you need a server to host content. I have been thinking about new models in this regard, but it hasn't been done before. Bitmessage is not public, and not organized in threads (a structured, sensible format with public matches of user : message). In fact there is discussions to ban meta-data from the blockchain. I'm not sure what the likelihood is. You can't host software on a torrent. Torrents are distributed data stores. Incidentally it takes a central initial access point (piratebay). You can't run software in a decentral way yet, although cloud virtual images to some extent do that. But in the end they are still servers owned and controlled by an account holder (SSH, linux user model).
By the way, everything on the internet, all URLs are subject to change. Most historic URL's don't work anymore, The blockchain is the first data store, where there is pretty high certainty it will not be lost.
Actually the history of Bitcoin goes back almost to the start of the (public) internet. The cyperpunks got started in 1992:
http://www.cypherpunks.to/faq/cyphernomicron/chapter3.html#2 at the same time PGP was released (as a book, because it was not allowed to be distributed as software). The idea of Bitcoin is much, much more than almost all people think.
The forum is in parts not a good representation of that. Unfortunately bitcointalk suffers from bitcoins success. Its the same as with reddit and why people flock to hackernews instead. same thing is happening here.
The server hosting is significant in terms of hacks, but also in terms of how it is structured and who has influence. For example the admin could decide to ban shady altcoins. But then there would be a debate what are proper rules for that.
One could do a lot of interesting things if one were to develop a new system from scratch with bitcoin as its core. If anyone wants to work on that let me know. The problem with doing something commercial is that it is not a good representation of an open community. But the forum itself certainly could be vastly improved. One could start with a fork of
https://github.com/discourse/discourse although I personally wouldn't use Rails these days. But the underlying software he is known to be crap and unsecure. I'm not sure why anybody is doing something better. Perhaps for the reasons mentioned - it is mostly uncontrolled and uncommerical. So it's up to us to improve it and see if people think its better.