Over the past decade, we have built a country-sized economy online where the default price is zero -- nothing, nada, zip. Digital goods -- from music and video to Wikipedia -- can be produced and distributed at virtually no marginal cost, and so, by the laws of economics, price has gone the same way, to $0.00. For the Google Generation, the Internet is the land of the free.

Which is not to say companies can't make money from nothing. Gratis can be a good business. How? Pretty simple: The minority of customers who pay subsidize...