Why do the missiles on an F-16 point slightly down?
If you take a look at the picture again, you'll see that the missiles are in fact lined up quite nicely with the nose of the plane. The missiles are not pointed down, they are pointed forward. The wings and engine (and the entire back two-thirds of the plane) are pointed up, which provides the lift to keep the plane in the air during normal flight. You can see pretty well the alignment in reference to the horizon in this picture (found by @jay-carr):



Just to cut off the potential comments about how planes generate lift, reference is here.