They just don't get it
Tablets running Windows have been out since 2001, they flopped. Bill Gates predicted it would become the most popular portable computer form factor. He was wrong, it's a tiny percentage of portable computer sales.
The fact is, you can't easily add extensions that convert a touch screen to behave like a mouse and keyboard. Even if it works you still have the problem of double click, moveable windows etc.
Also, you don't really want tiny multiple windows, small popup dialogs which go to the back of the stack if you attempt to click on and miss.
A WIMP GUI OS on a small touch screen is crap, it's lazy crap. Just get a laptop.
If you want a tablet machine then decide if the iPad does what you want or wait for some alternatives that run a 100% touch screen based OS. Android tablets will appear I'm sure of it, I'm sure Microsoft will come up with some Zune table running Windows Phone 7. Although they probably won't release it in the UK as usual.