The exclusives were paid for by Sony for Playstation players. It works like this. The xbox dlc is $19.99 for the listed content. The playstation DLC is $23.99 but Sony paid the extra $4 for their players to have the extra content. Thats as simple as I can put it.
Microsoft probably had the same option and didnt match or exceed Sony's offer.
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Also you can rage to Bungie all you want. Sony owns the rights to the exclusive content for the 1 year time period so its not likely to change anytime soon.