I remember hearing the game had been ready for months before they released and apparently they were going to release several DLC episodes, but instead decided to roll the content into a full-blown sequel and think they might as well not wait too long:
http://www.gamespot.com/news/6274256.html?tag=latestheadlines;title;3
http://www.gamespot.com/news/6274256.html?tag=latestheadlines;title;3