Is there a benefit to having the motors for a multi-rotor copter on the top vs the bottom of the frame?
It could be just for looks, but rotor placement has a noticeable effect on the behaviour of the quadcopter.

The higher the rotors are on the frame the higher the center of lift will be (the center of lift for quadcopters is the center of the plane created by the rotors.) A high center of lift means that the frame will be more stable. A low center of lift means the opposite. The reason for that is that the quadcopter can better naturally deal with lateral rotational forces on its frame. The center of lift being above the center of mass means that the frame is "hanging" like a pendulum from it. If you apply a lateral force to it, it will naturally swing back to place and the more you push the "harder" it becomes to move the frame.

A center of lift that is in the same spot as the center of mass of the frame means that there is no pendulum effect. This is like balancing a ball on top of another ball. All lateral forces, either internal like variations on each rotors' force or external like wind perturbations have maximum effect in moving the frame.

Contrary to what you might think, stability is not something you want in a quadcopter. The more unstable the frame, the more agile it becomes. Small variations in rotor force will create large rotational movements. The penalty you pay for that (small, unpredictable external forces also create large rotational movements) you make up with processing power. Processors are now so fast and sensors so sensitive that they easily can compute the external forces and create a response fast enough to keep the frame flying.