ANZ, the Boeing products that have slides on the wings are the 747, 757, 767, and 777-300. The installation of overwing evac slides are not dictated by the airline, but rather the design of the aircraft. The takeoff and landing flap settings are sufficient ramps for evacuees, and there is only a gap of a few feet between the ground and the bottom of the flap on the 737 and, in this case, the MD-80, even at the next lower setting from fully retracted. The Airbus narrowbodies are much longer-legged than their equivalent Boeing products, and it would not be safe to have such a large space between the ground and the wing. FAA and JAA pushed Airbus to install these on the A320, which is also what happened with Boeing and the 757.