Just when you thought you understood Web 2.0, along comes a theory so disruptive it razes everything in its path. The theory of cumulative advantage suggests that every successful Web 2.0 site — and the output of every Web 2.0 platform — is completely arbitrary and random. The head-exploding NYT piece by Columbia professor Duncan Watts is a must read, but here’s the key:

In our artificial market, therefore, social influence played as large a role in determining the market share of successful songs as differences in quality. It’s a simple result to state, but it has a surprisingly deep consequence. Because the long-run success of a song depends so sensitively on the decisions of a few early-arriving individuals, whose choices are subsequently amplified and eventually locked in by the cumulative-advantage process, and because the particular individuals who play this important role are chosen randomly and may make different decisions from one moment to the next, the resulting unpredictably is inherent to the nature of the market.

Oh, how sweet the irony — Web 2.0’s radical openness and transparency, combined with its intensely social nature, are precisely why it brings you the best of nothing.

Here is the most important line in the entire piece, which casts extreme doubt on every notion of democratized collective intelligence — “because the particular individuals who play this important role are chosen randomly and may make different decisions from one moment to the next”

In an open Web 2.0 system, with a randomly chosen group, it’s impossible to generate anything other than arbitrary results. Web 2.0 glorifies the “social,” but in an open system, social behavior becomes “monkey see, monkey do.”

All of a sudden it’s crystal clear what Web 2.0 really is — the greatest platform ever for harnessing randomly imitative social behavior. Before Web 2.0, achieving utterly arbitrary results took time and effort. Now, with platforms like Digg, we can get nowhere in a fraction of the time it used to take.

WOW — I am humbled and awestruck by the power of technology, and the power of randomly socialized human beings to snuff out each others’ critical faculties and personal tastes.

So does that mean Web 2.0 really is DOA? So long as it’s driven by the ideology of egalitarianism and radically transparency, probably so. But I suspect the pendulum is about to start swinging back from that extreme, so maybe there’s still hope.

I realize that I’m painting with very broad brush strokes, and that the fun I’m having with this theory comes unfairly at the expense of some of the myriad notions and sites that fit under the capacious Web 2.0 rubric, but it’s not everyday that you find scientific proof that a concept like Web 2.0 actually deconstructs itself.

As for Web 2.0 winners, is MySpace better than Orkut? Are A-List bloggers smarter or more interesting than Z-List bloggers? Is TechCrunch better than Mashable, ReadWriteWeb, and GigaOm? Are stories on the front page of Digg better than a bunch of random junk?

If you believe the theory of cumulative advantage, the answer is — NO!

Of course, this explains why Google has been the only Web 2.0 company to make a gazillion dollars harnessing human behavior, i.e. linking patterns — PageRank ensures that the link “votes” Google uses to determine search results aren’t from a “randomly chosen group,” and…it doesn’t show you the score.