Most times, the reasons behind dlc contents (whether it's additional content or videos/music/etc) is so that they can sell it on PSN for those who missed out or those who just bought the standard edition.
That way gamers have an option at a later stage and Sony can still make some money off it. It's a long running trend these days. Some pre-order incentive offer you a free dlc which can also be purchased on PSN for those who didn't take advantage of the offer.
Final Fantasy XIII
8 hours / Forever lost in the Matrix...precious.