From the official announcement:
Amazon.com and PlayStation are excited to announce that you can now visit Amazon.com to purchase your favorite PlayStation Network Content like Battlefield 4, Assassin's Creed IV: Black Flag, Call of Duty: Ghosts, and more. Amazon.com and Sony are teaming up to offer over 100 PlayStation 3 games, PlayStation 4 games, and downloadable content for purchase on Amazon.com. In addition to already released titles, you'll also be able to purchase the newest games and DLC the first day they are available for purchase using your Amazon payment credentials or Amazon Gift Cards. To browse this new selection, visit the PSN Store on Amazon.com.