Windows Vista Upgrade , no need xp ? True or false ?

Ive read the news from my website news ( in french ) i will translate how they did.

1) Launch the Vista DVD Installation.
2) Don't Enter your CD Key when the installation ( It will install the Evaluation for 30 day)
3) When you are finish and booted in windows, Launch the Vista Installation in windows
4)Enter your cdkey there
5)Do not choose Upgrade installation but Custom installation.
6)When you finish the installation, now active your vista.

They say they started from a formated brand new hard drive, without XP installed or XP cdkey.

Source in french : http://www.presence-pc.com/actuali [...] ade-21539/

I read about this via a digg.com link this morning. It appears to be true. Basically, this makes any upgrade version of windows into a full version. I'm wondering how/if they'll work around this issue. I've already picked up a OEM copy of vista for one of my secondary machines, just to try it out. But... this situation makes it tempting to pick up the upgrade copy for my primary machine sooner rather than later. If I don't have to invalidate my XP key I can switch back if things don't go well. I imagine the next batch of vista upgrade won't have this loop-hole.