Honestly I'm always a little surprised when I see, as it often seems to be, that GL doesn't have much of a visual direction for the artists to take, especially with important characters. He basically lets the concept artists roll and picks and chooses later. It's not that its wrong, but I would have imagined a stronger visual direction coming from the particular writer/director. Good web doc, as usual.
Seeing Grievous actually made be think about something, when you look at the all seemingly peripheral sidekick "Darth" villians in the prequels, when they are all taken together:
Darth Maul = Anger
Darth Tyranus = Dissention
Gen. Grievous = Mechinisation
When you put them all together, you have a perfect discription of the character attributes of Darth Vader. Probably coincidence, but a happy one.