People will find out soon enough that plopping down grandma in front of Windows 8 is not a realistic simulation of what people will actually see of Windows 8 on October 26th.
Firstly, most of these "experiments" were done on the Release Preview, where the intro tutorial video didn't exist to give people any hints about how to use the OS. The video has been extensively tested with real people as a pretty good way to keep people from getting stuck.
Secondly, marketing. There has been 0 marketing of Windows 8 so far. Enthusiasts like to think the verdict is in, the PR response is done, and it's time to move on, but the reality of the matter is that people know literally nothing about Windows 8. Real, honest to god people. The 99.9% of the world. That will change in the next 2 months before release, significantly.
Thirdly, and most importantly, grandma isn't going to go and install Windows 8 on her existing PC. She's going to go out and buy something new, build from the ground-up with the OS in mind, with the education included to teach her how to do simple things like "swipe in from the sides" or "move your mouse to the corners".