Think people won’t pay for content that is already available for free on the Internet? Sure they will.  This example from Ars Technica is fascinating: Ars Technica‘s John Siracusa wrote a 19-page review of the new MAC OS X operating system. He offered it for free at his site (where it got 3 million views) and as a $5 ebook on Amazon’s Kindle.In less than 24 hours, 3,000 copies of the ebook were sold bringing in a cool $15,000. All this for content anyone could read for free if they were willing to read it online or knew it was available online.So what’s this story about? Is it about the platform?Perhaps it is more comfortable to cozy up with a Kindle in a big armchair and read the review there and worth the price. Or perhaps the ebook is “being found” on Amazon by people who would otherwise not know it was online for free. Or is the Ars Technica brand one that has such an immense following that people want their own electronic copy.Neiman Lab talked to site founder Ken Fisher. “Ars has sold alternate versions of long-form content for 10 years, but Fisher said he underestimated the power of Amazon’s one-click experience, which makes impulsive purchases painless. ‘I was surprised by how many people told us they read the review online and they just wanted their own copy to go back to. Or they just bought it as a tip-jar kind of thing,’ Fisher said.”