The music business was always thought to work on the 80/20 rule as well, but lately there's been a general change of outlook about those numbers. In fact, many music marketers now feel that 90 percent of an artist's income (especially an indie artist) comes from only 10 percent of their fans.
The thinking in the 90/10 rule is that superfans (sometimes called uber-fans or your "tribe") are so passionate that they're purchase just about anything the artist offers for sale, and as a result the income is skewed more heavily in their direction than in other businesses.
There's at least some empirical evidence that 90/10 is indeed true, which means that for an artist to really break big, he has to move those numbers closer to the traditional 80/20 split. A superstar artist has to move those numbers even more. This is how it breaks out:
INDIE NICHE ARTIST
90% - income from tribe/superfan/uberfan (and anything else you want to call them)
10% - income from casual fans
MASS MARKET ARTIST
80% - income from tribe/superfan/uberfan
20% - income from casual fans
less than 80% - income from tribe/superfan/uberfan
more than 20% - income from casual fans
Once an artist establishes himself with a fanbase, regardless how small, the marketing goal from that point is always trying to move the 90/10 split closer to 50/50.
Check out my Big Picture blog for discussion on common music, engineering and production tips and tricks.