User blog comment:The Milkman/Dragonborn DLC coming to PS3 and PC/@comment-64.131.105.240-20121204222341/@comment-5149194-20121205035858

They have explained themselves. Xbox and PC use DirectX programming, which is the primary format they make 1st, it's apparently easier for them to create games with. And it's hard for them to transfer it. (someone besides another 'wikia contributer' correct me if i'm wrong.)