Apart from the features, I think nowadays people are more comfortable
joining a forum than subscribing to a mailing list.
--
Nathan Whitehead
And then you have the other class of people who prefer to manage their own moderation, get all of their communication in one place, have an easy way to search through all communication regarding several projects, and not have to remember the links to half a dozen forums.
And then there's me who will subscribe to all of the mailing lists and put the forum in a permanent tab on firefox :)
But it's true - there may be a potential audience that we are not hearing because they don't follow mailing lists.