I don't know the type, but I can think of a few reasons:-
(1) PEC mean that it isn't as high as 1.85 Vs
(2) The large drag flaps that I can't help noticing on a 172 may well permit a steep high speed approach, with speed bleeding off very rapidly in the flare, and that low speeds would jeapordise control in the flare. This is certainly broadly true of the C150, which I've flown a couple of times.
G