The mailing list is the heart of the lug. I doubt many would argue that or wish to change it.
I have no issue with Facebook and use it a lot. (Just accept that anything you post on there is no longer yours)
I have "liked" the DCLUG "group" some time ago, but it's worth noting this is not a "group" in the Facebook sense. It's just a page. You can't join it, it doesn't show in your list of groups. This setup is generally used by businesses to broadcast, rather than a community to discuss. Perhaps that's the intent and if so, fine. From the messages in there, many won't use Facebook so it won't ever replace the list and perhaps having a Facebook Lug community would split part of the community off, so probably best left as it is.
I rarely visit the website(s) any more but if a plugin to auto-post articles/pages to facebook was added, it would help me keep abreast of things. Certainly the website(s) should remain and be a center for news and information, including interesting articles, because it's searchable and a reference in a way neither list nor facebook can ever be.