I found this fascinating quote today:
Employers pay for that expertise in the form of a salary. Audiences pay for books written by people who have detailed their experiences or knowledge. University tuition costs money. And you can argue all day long about how to determine the value of learning and how to filter out the good from the bad. But the fact remains that experience and knowledge can be worth money, and those that have it have reasons to put a pricetag on it.altitudebranding.com, 3 Reasons Why Expertise Costs Money, Feb 2010
You should read the whole article.