I think if I recall correctly; they stopped doing real-time performances on stage demos after all the snafus and weird bugs that can crop up. I'm not sure if you recall some of the issues with some UC4 E3 play throughs where they crashed at opening the door and needed to reboot. I believe that was the last time Sony ever decided to go with a real time demo.Impressive, but... "in-engine". You can render at slow 15 FPS and then double it and play it as a smooth 30 FPS video, and other stuff. I'd like developers to show us true real-time stuff. I don't like to wonder how much of that will be seen in real-time.
The 'in-engine' trailers you see for both Sony and MS are running real-time on the hardware, but then recorded and likely edited (perhaps scene reversals, timing of audio, trailer/order changes) to ensure that it runs flawlessly and on-time for the time slot they are given.
I think there have been a great deal of many moments where people were in disbelief that it was running in real time; but I think all/most of them came through.