User blog comment:Saratje/PC release date explained - Skyrim: Dragonborn DLC/@comment-81.144.132.166-20130107141925

It wasnt delayed, microsoft had timed exclusive. Bethesda stopped refering to it as dlc so that they could give to to microsoft because the 'deal' was that they could have two pieces of dlc as timed exclusives so if they stopped refering to hearthfire as dlc they could give it to microsoft as well as what they are now saying are actual dlc's namely dragonborn and dawnguard. so basically, it seems that the 'goal posts' were moved to benefit microsoft and bethesda got paid likely a large amount for this.