Oh, on the question of character motivations and Captain Titus:
There is a good story to be told about a character bound by duty, if you do it right.
I mean, if you try to look at WH40k with a straight face - you see that a life of everyday human in this world is an endless horror of backbreaking labor, mind-numbing imperial dogma, draft army that thinks nothing about it's losses, you can be killed several times over in your lifetime for crimes of thought, and literally dozens of nearly omnipotent enemies, that can whisk your life away at a whim.
You have immortal (let me spell it out - i-m-m-o-r-t-a-l) gods of Chaos, that can find their way into hearts and minds of anyone around you, you have Necrons - sentient machines awakening from slumber and bound on eradication of all life in the universe (sounds familiar Bioware?), you have a living tide of destruction called Tyranids, you have unpurgable infestation of orks, who seem to survive and come back no matter how carefully you cleanse the solar systems from them.
So what keeps Imperial citizens from dying of pure horror the second they think about all this? Faith - they believe that in their deaths they'll be happier than in their lives, and duty - each of them believes, that they are born to fuel the life of humanity as a whole, that people should give their lives so that the greater Humanity lives under endless onslaught of it's foes.
Again, you can tell a good story about a character, whose only way to stay sane is to have faith and believe in his duty. I am not saying that this game got it right, but you can. You need to really describe the unspeakable horror of the world around such character, and show how following the simple truths allows him to live in such a world.
Just because a lot of characters say "Duty" in their lines, doesn't mean that we have a lot of characters that are defined through their sense of duty. Mostly they are not, they are just bland and say words without meaning it.