As I understand it, the Dark Ritual scene was originally supposed to be a little more reactive to the player's relationship with Morrigan, one feature that didn't make the final cut was a kiss sequence for wardens that romanced Morrigan. This extended kiss sequence was restored in line with the VO/scripting notes to give a little more impact to the scene for players who romanced Morrigan. There's no new dialogue and the scene is restricted to wardens who have a "Love" affection rating with Morrigan.
This scene and more can be restored to your game via Terra_Ex's Morrigan Restoration Patch:
http://www.dragonagenexus.com/downloads/file.php?id=1120
http://www.youtube.com/watch?v=s6P613D3fv0
