Some people just never notice certain parts of UI. There are millions and millions of people with iPhones and there is likely going to be someone who just learned about the camera-switching icon for the first time.
Plus, that same video showed people that you can use the volume buttons as shutter buttons which is something most people likely don't know about.
it's not they don't notice, they don't care and don't use all the functionnality. They are quite stupid. (feel free to downvote me) but I think the same, "how to do simple" things is useless. If the user don't want learn something new, why they will see a video about it?
At the end of the day, UIs are unnatural interfaces. Skeumorphism only makes things worse. So UX design can only meet the user half way; intelligence must be employed to get the most out of an interface.
I see these videos as akin to using a TV remote instead of getting up to change the channel: people are lazy, so appeal to that laziness (along with the whole "here have some pro resources" thing as well) as a form of sales.
Very useful, I really liked that design. (If anything, I wish there had've been a little "notch" cut above the right edge, so that once you move the slider over and the top and bottom parts animate out the edges of the screen, it would look like the slider was moving through the notch. Hopefully that made sense. I do realize that such a visual design would have been just confusing enough that it would never have been approved, though.)
Plus, that same video showed people that you can use the volume buttons as shutter buttons which is something most people likely don't know about.