Meta filter is a pretty unique online community in that it is a very large group of people who are sincerely helpful in a almost unlimited number of subjects. As the article says, there are many much smaller cases of similar actions of humanity and helpfulness on askmefi on a fairly regular basis.
It would be great if the proliferation of this type of online community was the future, but Mefi has been around for a long time and, in my opinion, truly separates itself from the rest in terms of helpfulness of the commenters and consistent quality of the content.
HN and some other communities are equally helpful from time to time, but I have come across none that match Mefi in consistency and breadth of subject matter. (obviously HN isn't trying to match in breadth of subject matter.)
I guess what I am saying is that with most online communities I accept that the other people won't necessarily act with the same compassion as they would with friends they have IRL. Mefi has done a pretty extraordinary job maintaining a community in which this standard of human decency is pretty well kept.
tldr: Mefi is a unique online community in that it's community members act more like they would IRL in confronting one another's problems.