I think you're oversimplifying the demo. Things that clearly impress people are the realism, the cleanliness (possibly 'fake' as not in game) and framerate (likely true in game, or at least presently a target, as you wouldn't create 60 fps cutscenes for a 30 fps game), and general artistry. The clothing appears to be modelled at a mesh level instead of just tweening normal maps. The water in the background moves and is shaded very realistically, but the DOF can help with that. The flora is remarkably detailed and moves convincingly and, for those extrapolating the cutscene to the game experience, is suggestive of the same in game.
Overall it is very impressive, as a cutscene, and a progression of standard technologies in realtime graphics. A game doesn't have to reinvent rendering to be able to be impressive. It's also worth noting that the beginning of the trailer reads, "the following trailer was captured directly from a PS4," implying a stronger, though not conclusive, connection with being realtime.
Personally I think the jaw-dropping either comes from a fairly emotional response due to the artistry and enthusiasm for the IP, or a belief that the game itself will look just as good. Those with positive responses are entitled to them - they're not stupid or sheepish or anything. I myself will not extrapolate game experience from a PR trailer. There's lots of precedent to show that trailers designed to get you excited aren't a good measure of what the final game will be. The trailer should be measured as a trailer, that just happened to be rendered on a PS4.