Apparently you can just buy a copy, no upgrade applies. You need to clean off your previous install anyway AFAIK.
Got a copy on order.
Depend where you live
Youre getting the full, were only getting the upgrade for the promo price.
The issue with the UK version seems to be removing IE from the install, its simpler to do a full install than try and remove it.
There is also the issue of reinstalling a dead OS so I cant see them producing a disk that only upgrades over an installed system. Even if there is only an install over option it should be easy enough for someone to accidentally post you a copy of the Vista install disk they have been keeping as a backup instead of the blank disk they were going to send...