I agree with you for the most part. I too think that online communities work best when there is a component of that group that exists in the real world. My class presentation was actually on the creation of local attachment based on meet-up groups online.

I would like to answer your first question:
I think that the main difference between online communities of the past and those of the present day, is that now you can find a community that matches many nuanced interests of your own, rather than the ‘one large room’ of the past telegraph, usenets and such. As time goes on the communities in which we inhabit both online and in the real world are becoming much more specialized.