The difference between typing and moving to use a mouse or trackpad, is that your arms / hands / fingers do not have to change from the horizontal to vertical axis - meaning it is an easy shift physically, because your arms can remain supported by the desk. As soon as you have to lift your arm to touch the screen, and not just touch, but interact using fine motor skills, it is simply more difficult to do and therefor less efficient for work.
I think people want to want touch screen laptop and desktop computers to work, because we see movies like Minority Report, where people are [sort of] interacting directly with the screen, but in actual use cases, moving back and forth from keyboard / mouse / trackpad to touch screen is inefficient at best. And I say this as someone who has tried to make it work using the iPad and BT keyboard.
I don't get comments like this. It would take you 2 seconds to test and realize that you can touch every point on a touch screen laptop without raising your elbows of the desk. I can touch at least the bottom third without even moving my elbows from the position they naturally rest at while I'm typing. In other words, on a theoretical touch screen macBook, I'd be able to fully interact with at least the dock without making any changes in my hand/elbow position.