[Begin cynicism] I've got it - they aren't giving them away, not now, not ever, and they never planned on it... They let it "leak" that they were going to do this to get people to sign up for Prime! [End cynicism]
It actually makes sense though, the easier it is to get them, the more people there will be with Kindles, the more people with Kindles the less people will be inclined to get an iPad, the less iPad users as compared to Kindle users means Amazon gets to keep a lock on the book sales.