It's not just a different light bulb, it's a whole system including a high voltage ballast and possibly a whole different housing assembly altogether.
Originally Posted by Ox-y-GenIII
Could Ford just build a customers ST3 without the HIDs and then have them bring it to the dealership later to swap out? It's two screws, wouldnt take long at all. And they could resell the used lights to body shops for OEM replacement lights.