Ah, OK. I clicked the second link, but I didn't notice the first one. It didn't occur to me that you meant anything other than a regular Wacom Tablet, since I work with those all the time but have never seen a Display version.
I've never seen someone use one of the Wacom tablets with a screen, but I've looked over the ads before. They're really expensive, even compared to a Tablet PC (which is costly, but better than a tablet and a laptop seperately). I got my Tablet PC refurbished, so I'm sure prices would be somewhat better on the Display Wacom Tablet, but I doubt it'd be a better deal overall.
They are better quality, though. If someone cares about super high accuracy, pen pressure, and all the other stuff that high end Wacom Tablets are good for, then they're the way to go. I don't care about any of those things, so my comparatively less expensive Tablet PC works very well for me. I have a lot of friends and coworkers who'd probably feel nauseous trying to work on something as low end as my machine, though.
Like you said, Erzengal, Tablet PC is mainly more useful in the situation that our beleaguered artists describes, where he's trying to throw something together on the road. It'd be pretty cumbersome trying to carry around the Wacom tablet *and* a laptop.