Thinking about it, you have a very valid point, there must be something that does scratch one's screen, grit in the pocket perhaps? I must admit that as far as I know I have never suffered scratches on the iPhones that I have owned, it could be that my 57 year old eyes do not pick them out (A very good possibility TBH).
What I will say is, that if asked what in my opinion was the iPhones biggest flaw, scratch resistance on the screen would not be near the top of faults that I would want to be addressed. I think the iPhone would be nigh on perfect if the water resistance was tackled first, the rest, IMHO is the icing on the cake of a superb phone.
We all know phones that get scratched from things like keys and other types of metal in the pocket. Yet his isn't supposed to happen according to the scale with phones covered in gorilla 2 or 3. This reviewer is just a kid with no discernible experience or credibility. Even if he has a real prototype iPhone 6 front, it means nothing because he doesn't understand basic testing. Why not compare the scratch resistance to Samsung s4? If iPhone 5s uses gorilla glass 2, then this iPhone 6 material is probably no better than gorilla glass 3 which is supposed to be 40% more scratch resistant. This was never made clear so the video is just as bad as the first.