Hard to know if Porsche holds back its best stuff as a marketing stunt, but I doubt it.  More likely, new models have a certain development/production budget and timetable, and at some point the designs have to be signed off on and produced.  And while I may also question the facelift process, I also realize that between facelifts Porsche does offer new options for customers who order the "pre-facelift" models...