Sterling walks through Gearbox's walkthrough of Aliens: Colonial Marines.
That is, the Aliens: Colonial Marines Gearbox wanted the world to believe in, not the one that actually happened.
While demo footage is not representative of the final product, it isn't supposed to be more polished, better animated, boast superior features and be almost entirely comprised of sequences that never happen in the game. A vertical slice of gameplay? A reasonable excuse ... if the gameplay being sliced as actual gameplay, and not an entire fabrication.