According to
this article Kindle owners have found an effective way to voice their displeasure with publishers delaying the release of books in the Kindle format. They're giving the book 1 star reviews.
This may not impact the sales of a book like "Game Changer" that is expected to receive polarizing reviews, but it could definately have an impact on sales for other books. Amazon's rating system is a vital tool used in marketing a book, and pissing off customers, especially heavy reading Kindle customers, may not be such a smart idea.