It looks like that because it's actually a functional spoiler. It's built exactly like an airplane wing... an upside down one.
As air flows around the spoiler, it speeds up as it takes a longer path to travel underneath, therefor creating a low pressure area. The air above the spoiler has a shorter distance to travel and is moving slower, thus creating a higher pressure situation than the air beneath it. The difference in pressure pushes down on the spoiler and keeps the rear end on the ground. Tilting has nothing to do with it.
I liek teh physics.
