I'm not sure this outlines the 4 dominant models. It strikes me more as the dominant business model (per-click ads) and 3 ideas that are novel and popular. The latter 3 haven't proven themselves as "Business Models". There is no particular indication that they won't go the way of (e.g.) Google's custom search: a good idea at the time, but unfortunately not particulary relevant to the market in the long term.
I suggest adding the prefix back in to the title. Without "Monetizing Social Networks:" in the front, the title is wrong, as the classic "make stuff, then sell it for a profit" doesn't appear in the list. This article is far more limited than the HN title suggested.
Yea, I tried, but It got cut off -- character limit.
I'll cut out some other thing.
Edited. That's better. Now it includes the social networking prefix
Freemium should be on there, too, which is how LinkedIn makes some (most?) of its money. Many dating sites fall into this category, too.
An interesting overview. I'm not sure of the validity of taking all of your statistics from TechCrunch, however.