Yeah, you still have to break away, but Stubborn just makes it more unlikely you'll get to that stage. I4 isn't bad either - falling back from a charge by Ork Boyz or Necrons isn't too difficult if you're testing on Ld 4/5.
It's also the fact that as a shooting army, you don't want to engage enemy melee units - if a squad of Terminators with Lightning Claws charges your Tactical Squad and kills 9 of them, that one dude is going to hang on with Grim Resolve, die horribly in your turn, leaving the Terminators free to do what they like next turn. There is a minor plus that if you charge someone and the rolls go horribly, you stay in combat during the enemy turn, but it'd need to be a pretty wacky roll to go that badly for you, and you'd need to be charging with Tacticals in the first place (which means the enemy is either very weak in combat or you're on the win anyway).
In short; I don't like Grim Resolve because Dark Angels really like breaking from combat.
Last edited by MidnightSun; 10-15-14 at 03:20 PM.