This is simple. Because of it's clear, fast & simple feedback, or in layman's terms - it clicks The d-pad may not be sexy, but it's really fast to use because it's located conveniently under the thumb (N800). It's easy and quick tool for navigating in menus. It also works well together with the touch screen, for example I might open a menu with right thumb, and then browse and select items with the d-pad.

The usability is emphasized when using the tablet on the move like walking. It's a lot easier to navigate with the d-pad, because I don't need two hands and I don't need to look where I touch and I don't need to verify visually on the screen that the touch is interpreted correctly.

Even though palm's latest doesn't have a d-pad, their earlier PDA line and OS made the usage of d-pad an art. You could do pretty much anything with it. The fact that the latest competitors don't have it doesn't mean that it's become obsolete. It just means that the UI people don't know how to utilise it. D-pads might also be seen as too old and boring technology for a hype product - a bit like our old fashioned keyboards, but they aren't going anywhere.

The way I see this is that the challenge for Nokia is to make a d-pad that is useable, but still sleek looking to please the modern consumers aesthetics. (For example the Motorola Razr's d-pad failed terribly on the usability part.)

For goodness sakes - you have d-pads on all your mobile phones as the main navigation tool. Do I really need to point this out?!