Afaik the game actually scans your system and sets the options at what it thinks will run best on your system. If the portraits are off it's because they don't think your game will run smoothly with them on.
That could be. It just seems odd to me that it would have that setting when my computer has no problem with any of the other game animations, and that's not an issue with the portraits in my copy of the original game.
* shrugs *
