The Wikipedia Long Tail entry carries a graphic that describes it:
The Wikipedia Power Law entry is graced with:
Clearly the two are (very) closely related. What's important, however, isn't that this relationship between a dominant few and an easily overlooked or disregarded majority is a "law of nature". Whether the division is really 80-20 is highly debatable and it's a good guess that many cases get squeezed into that ratio even when it doesn't really fit. What's important is the fact that once a relationship of this sort has been established, breaking out of it - not only falling out of the elite, but especially working up into that privileged few - is incredibly difficult. If at one point the web held the promise of more exposure for the overlooked majority, today that seems little more than wishful thinking.
