The things you see at the leading edge near the wing tip on the DA20 aren't stall strip, but rather turbolators. Their job is to increase aileron effectiveness at low speeds - and DA20 is indeed fully controllable only with ailerons down to stall speed. The DA20 actually doesn't require any actual stall strips (near the wing root as you mentioned), because the stall is actually quite benign, until/unless you help with rudder
The turbolators change laminar flow to turbulent flow, thus delaying separation point and making ailerons still effective at low speeds. Since detailed aerodynamics is not really my field of expertise/interest, I'll leave more detailed explanation to someone else
