The problem with a book like this, and books like these in general, is that they are books. To read them requires that a person actually spend the time and money to procure a copy.
Who is going to do this? The people who already know (or strongly suspect) what is in the book and approve of its message.
I know the authors want to make money from this book. They spent time and money of their own to research and write it. But if they really want as many people as possible to be made aware of the information they have uncovered, posting that information to blogs and other websites is the best way to disseminate it.
The truth matters, but truth that people are unaware of is truth that cannot help them. If the average American had good knowledge of who and what Obama is during the Dem primaries, he wouldn't be in the White House now. We might have Hillary instead because McCain was such a loser, but we wouldn't have Obama.
Modern politics is an information war. The lefties control most of the media and use that to block and distort the truth while promoting lies. Writing a book that will only be read by republicans, conservatives, and libertarians, and even then only by those eager to spend the time and money to do so, is literally preaching to the choir. They already know that Obama is bad. They buy and read this book to confirm that assessment of him. Independents and honest leftists (also known as future libertarians) won't get this information because they aren't looking for it. You have to put it out there where they are likely to encounter it, or at least encounter someone from the left trying to discredit it.
Think for a moment about the stings that brought down ACORN. Had O'Keefe and Giles written a book about their experiences, instead of providing video on the internet, nothing would have happened. Breitbart uses the power of mass media to get the truth out there, and the authors of this book should consider doing the same.