WHS is based on Windows 2003 Server, so yeah it has more in common with XP than Vista.
While this isn't 100% fire-and-forget for users, it's pretty darn simple. If the product takes off, I wouldn't be surprised if in the future there was a 1-step config for a WHS box. Plug the box into the network, turn it on, run an installer on your PC and *boom* it's all auto-detected and setup. No harder than installing a printer probably.
Personally, while the price on the HP is very attractive, I'd probably prefer to just buy a stand-alone copy of WHS and another hard drive and slap it into a spare PC. But for those who don't want to bother with that hassle, the HP prices are impressive.