It makes sense. A crash is just an extreme deceleration. To have good odds of surviving one, your body should slow down at the same rate as the plane. If you're facing forward, the only thing slowing you down with the plane is the seatbelt. If you're facing backwards, you have the entire back of the chair to slow you down. The deceleration force is spread over a larger area of your body, making it less dangerous and keeping you from hitting your head on anything.