The Character Arc

Every character has to have an arc. Every character must go through a change. If our characters don't change, it's not a story about a character; it's just a description of an event. But how hard and fast is this rule? What about character's who are on the brink of achieving that epiphany but fail to complete their arc? It seems tragedies are built around those flawed characters who come so close to seeing their error of their ways but fall short. 
And what about those stoically awesome tough guys who solve all their problems with violence? Do we really want to see an Arnold movie where he learns to overcome adversity with creative thought and the application of empathy? Or do we want to see him stick to his guns and be a bad ass until all the bad guys are dead?
Character Arc is important. So important that it should be discussed. I think there's more to it than just "The hero has a flaw, but through the course of the story, he'll overcome that flaw." What do you guys think?