Alex Tabarrok writes in Marginal Revolution:
[. . .] Rowling's success brings with it inequality. Time is limited and people want to read the same books that their friends are reading so book publishing has a winner-take all component. Thus, greater leverage brings greater inequality. The average writer's income hasn't gone up much in the past thirty years but today, for the first time ever, a handful of writers can be multi-millionaires and even billionaires. The top pulls away from the median.
The same forces that have generated greater inequality in writing - the leveraging of intellect, the declining importance of physical labor in the production of value, cultural and economic globalization - are at work throughout the economy. Thus, if you really want to understand inequality today you must first understand Harry Potter.