I do agree with that point. But I think we are in a period of time where we have a mix of old and young folks and it hard to find that “tool” that will work for everyone. The problem, which was said above, that the information can be easily scattered.
To me, I think just having a wiki with the basic information (what the team/project is, how to get involved, ect.) and use the mail-list for all of the discussion. IRC could be used but I feel like it would be better off used just for meetings where you can get many members on at the same time to talk.
Forums can get too large and to hard to follow for support, so I do agree that for support (Q&A too!), stack exchange can work. I see forums just acting like another mailing-list like environment, that could be easier to follow and to reply to if you don’t have the e-mail.
As for social media, you need to find a way to sync what you will post, if you have multiple places that will post.