I never suggested replacing a discussion list with social networks, and furthermore, I never suggested that email lists are archaic, or outmoded. I don't think they are at all, but I do think that one, the perception exists that they are, and two, while email lists can be used for group discussion, and perform adequately, other tools exist that are better suited to support group discussion in today's web.
The point that I am making is that given the need for electronic distribution of information to a community, different tools are going to be better fits, depending on the type of communications going on. If this is done well, the community gets to forget about the method of communication entirely, and focus on their content. It isn't a difference between wrong and right, but a difference between good and better.
Do you need to distribute bulletins and announcements to a large list of people? Email lists are where it's at, especially in conjunction with another network to point people to the list.
Do you have a finite, manageble number of people that are going to be producing content, or serving as a gateway for a larger number of contributers? You want a blog. You can have a blog that isn't focused on the individual, for example, Huffington Post, or any of the New York Times' blogs. Keep in mind that the larger community also is able to interact and discuss the content.
Do you have a community that doesn't need any kind of centralized content management? Go for a forum. This is the most flexible option, but also has the most maintenance requirements.
Do you have an existing community, that's already using a tool that works? Then don't fix what's broken, unless there's some kind of external motivation to change. I've been a programmer for far too long to have any sort of interest in creating a solution to something that isn't a problem.