If you don't remember it then you haven't watched the show very often. The shoulder extensions have always been there and every model made for SFC has had them. They were even on the concept model the FX guys made before filming ST3. Also, nobody said anything about the torp launcher itself being wrong, the discussion was just about the color and appearance.
Exhibit AExhibit BExhibit CThe ones on mine are close to the original (aside from the subtleties in having to build everything by eye and lower detail) and I doubt anyone would have spent so much trouble making them if it wasn't supposed to be there. Heh, six years doing this and people still think we modeler types would miss such an obvious detail. Ah well, at least it distracts from the stuff I really missed...
And yeah, in the TMP movies there was a physical torpedo in the launcher - the cheap fx for ST5 allow you to even see it flying toward the Enterprise. I was speaking in general terms since they seem to have tossed that idea by TNG/DS9.