I think that what differentiates a Win 8 tablet from say, and Ipad or an android tablet, is that you can use all the handy touch features for every app that works best with touch, and then still have a complete pc computer when you need one. Plus handwriting recognition, doodling, and touch document markup in Word and OneNote, etc.
Therein lies the beauty of a clamshell tablet pc: when you want to, you use the keyboard and touchpad, and when you don't you just use the touch screen (and stylus if you've got one). The screen reverses and lays flat, so you can lay it on your desk and work away. Or, if you don't want a huge headache in a few minutes, the keyboard works as it's own screen stand so you can reverse the keys away from you and tilt the screen to an optimum angle and just use touch. -- this works especially well on Airplane tray-tables, lounging on the couch, or at narrow coffee shop countertops.
Granted, the clamshell is more expensive than a slate, but if you consider the savings in external mice and keyboards, screen protectors, and stands (not to mention the reduced hassle in having to carry all that junk around) I still think the clamshell is the better buy.
I love my touchscreen. I wouldn't want to give up my keyboard, as this is not so much my primary work machine as it is the machine I use most often to work. But with a clamshell tablet you don't have to.