You aren't suppose to move your feet until the release. Not being familiar with the video, boot blades assist in keeping your feet set. People that have an Olympic hammer throwing back ground rarely use boot blades and tend to shift their feet some, but not enough for the judge to call a foul.
http://www.youtube.com/watch?v=Ln9KeZNr7L4 Here's a somewhat grainy video of a Pro competition where you will see some minor and major feet movement but mostly during the release. The heals may move during the throw, but the feet do not shift.