Why are the B-52's vortex shedding panels angled?
The angle of the edge shapes is such, that as the spoilers are stowed, the edge shapes are aligned with the airflow over the upper surface of the wing.

If the shapes were perpendicular to the spoiler trailing edge, they would form an angle of about 35 degrees to the airflow. This would cause turbulence, as the spoilers are not retracted 100% flush with the upper surface of the wing. The turbulence would lessen the lift of the wing and the effectiveness of the flaps (shown extended in the picture), and add drag.