User blog comment:Jimeee/PS3 release dates for Dragonborn, Hearthfire and Dawnguard - Euro Update/@comment-24901571-20130203063944/@comment-182.239.130.102-20130203072159

I believe they are doing it this way as more of a 'best foot forward' kind of deal. Xbox user have widely regarded Dragonborn as the better of the current DLC's, and they want to put their biggest hit out first.