Last year in my Structure of Fiction class, there was one day where we got into a discussion about authors having Facebook. Our professor and several classmates expressed their frustration at not being able to find out more about their favorite authors because they didn't have a Facebook they could creep on or a Twitter account they could follow. It was usually little to no comfort if the author had a Wikipedia page because these tended to provide scant information. Everyone owned that not being able to read more work by their favorite authors online made them itchy with expectation for that person's next book. They would buy it as soon as it hit shelves or the "e-store" because, by not having an internet presence, the author had found a way to make him or herself scarce--a commodity.
After discussing this, our professor noted that when a person is just starting out in the business and trying to make him- or herself known, they should do the opposite. Status updates and Tweets galore. Anything to get themselves on the map, to get noticed. Foster the People is a great example. Band founder and frontman Mark Foster did everything he could to get a record deal in the ten or so years he was camped out in L.A., a face without a name. He would sit in the corner of Hollywood parties with his guitar, hoping to attract enough attention that some famous person who could give him his big break would walk by and take an interest in him. Posting a free download of his band's song "Pumped Up Kicks" on the web was what finally launched him into stardom. The song became an instant hit and pretty soon a producer was asking his band to write an album around it. That was 2010. In June this past year, I paid fifty-five dollars to go to a concert so I could hear the new stuff they were making (a hard rock version of "Pumped Up Kicks" was a highlight). In two years time the band became superstars because at first they cast far and then later reeled in tight.
My guess is the reason why iBooks Author is currently free is because of this same "cast far, reel in tight" strategy. First, you have to publicize yourself and what better way to do that than to make your product free? Tons of people will download your product if it really is all that it's cracked up to be and suddenly you have a fan base. To extend the fish metaphor, your fans are then "hooked." You can start reeling in, making yourself scarce, making yourself a desired commodity, charging those little fish. And hell, they'll pay. Because by broadcasting yourself far and wide in the initial stage, you now have them hook, line, and sinker.