Friction is also variable, with pen and paper type. Although the iPad is a bit too slick, it gets very fatiguing (I did most of my HW in college on the iPad)

It may be the case that the iPad is slicker than ideal for some people, but even if that's the case it doesn't relate to his point about centuries of adaptation or whatever. In the past, we were limited by the laws of physics and the materials available in our environment. If people could have had whiteboards 200 years ago instead of chalkboards, they would have taken them (easier to erase, no chalk dust). But they didn't have them, so they didn't use them.