User blog comment:Jimeee/Dragonborn DLC trailer released./@comment-124.150.79.54-20121105203604/@comment-1992639-20121105204445

Exactly. Hearthfire was an extra. Maybe it was intended to be part of Dawnguard at first as both Dawnguard and Hearthfire content originate from the game jam. Microsoft may have pushed for a deadline, opting Beth to release housing as a separate content pack.