Here's an update. My dealer and I went round and round in a friendly way, trying to resolve the missing deflector. We looked at at least a dozen Explorers and couldn't find a single ST or Platinum with the Air Deflector. Every EXT and and Limited did have the deflector.
I think all of the explorers should have the part since without it, the bumper facia hangs loose. Mine rattles when I tap it. I do foresee something hooking on the bumper and ripping it off. Regardless, The dealer didn't what to pay for one but we did compromise. I'll bought the part, they'll pay for the install. That part is backordered into March and the parts list does not identify all the nuts and bolts that attach the deflector. Guess the dealer will figure that out.
After ordering the part, the head of the service department hunted me down to advise me that Ford likely has a good reason for not using the deflector on the Platinum and adding it might result in unexpected consequences. Trapped heat being one. Who knows, it might not even fit. But we'll see..