It's all about flexibility and versatility. The interface is more or less irrelevant, it's the way in which the device can be adapted to different usage situations that's important.
- A desktop is relatively inflexible, it sits on a desktop unless you're very adventurous, or a gamer with a specifically designed gaming box.
- A laptop introduces significant flexibility, but is still constrained by bulk and a more or less limited degree of screen positioning.
- A swivelling screen notebook (something that is problematic on a large screen notebook), introduces greater flexibility, but works best with small form-factor screens, which may not be an ideal viewing size. And they can still be relatively bulky.
- A tablet provides for a very flexible device, that can adapt itself to be a laptop/notebook as well as a light-weight large screen computer.
The notebooks are pretty much fading away, as a tablet can provide much the same capability and flexibility, in a much easier to use package.
My Fujitsu 8.9" screen notebook weighs 1.2kg on it's own. My 10.1" screen Gigabyte tablet with keyboard cover weighs 1.3kg and without the cover weighs 0.8kg (the same dimensions and weight as the Surface Pro - but with much more flexibility).
So using a bit of imagination, one can see that the tablet can offer a great degree of versatility over desktops, notebooks or laptops. The touch capability is neither here nor there, it's what UI works best under the circumstances. To give an example:
This is how I use my tablet when I go bush and use it as a off-road navigation device. Touch is pretty useless in this situation, as the navigation program does not have great big finger friendly controls when bouncing around bush tracks, or not. You can move the map about with touch, but for everything else I use a wireless mouse, which is infinitely better. It's not something that you can do with a laptop and even the Fujitsu didn't work all that well.
Then I can take it out of its cradle and use it for further trip planning at camp, download and look at photos I may have taken during the day and even connect to the internet and see the latest good news about how Windows 8 is faring, or not (thankfully, we're usually well away from any internet connections for that).
So you see, it's the flexibility and versatility of the device that's most important, not touch, which is really quite irrelevant and over-rated in the big picture. That is, if you can think outside the box.