Re: Perhaps a metaphore will help you
"Why does a car have a steering wheel, a bike handle bars and a horse have reigns?"
Reading some of these comments almost makes me ashamed to work in IT. A car, a horse, and a bike have completely different methods of movements and working. You turn a bike by leaning and steering the front single wheel AWAY from the turn (at anything other than slow speed), while a car is turned by turning the front two wheels IN to the turn. Just because they both "go" doesn't mean they work the same way. Similarly, the throttle on a bike has much more control than just "faster/slower". Throttle control is critical to control and stability of a bike through a turn, and even in a straight it is vastly more important than in a car, hence the requirement for a much more subtle touch (and hands rather than feet). A horse, well, obviously a horse is an animal so you give it an instruction and hope it goes the way you want it to. However you slice it, you are going to have to learn three methods of operation because they are all completely different beasts that are made to "go" in fundamentally different ways.
A PC/phone/tablet pretty much all work the same way. In all cases you input instructions (typically via a keyboard and/or mouse but these days also with a touch screen (either as well or instead)) and tasks are run on the CPU, data is retrieved and processed, and displayed back to you. The difference is purely device size. Some are convenient to hold in one hand, some are not convenient to hold at all, but a 8" Windows tablet works the same as a desktop with a 40" screen running Windows. The same for Android. The difference is that some (most these days) smaller devices (phones and tablets) have a touch screen. Some laptops and desktops also have a touch screen. That is often an additional control method, or a replacement control method. However, if you know how the OS works, and you how to find an application, start an application, control and application etc, whether you do that by pressing on the screen with your finger, or moving a mouse pointer there and clicking, IS THE SAME. The difference in required learning between leaning a new way to activate an appilcation (press with your stylus or finger vs click with a mouse) is much less than learning a new (going from an XP like interface on one device to a Win8 interface on another).
I thought all that would be obvious, but I guess not.
As for a touch screen on a desktop/laptop, it is an ADDITIONAL interface. It doesn't stop you using a mouse or keyboard. It isn't one of the other. Having said that, why don't you ask people who have worked with touch screens for years? Certainly the ones in the ticket office at St Pancras find them very useful, but I suppose they haven't been told yet that they should be having back pain etc.
It is just like the Kindle e-ink debate. The number of times I have been told that I must get eye strain by reading from a tablet instead of an e-ink... The same tribal blinkering here.