I don't expect all these questions to be answered right away. Gradually over time is fine. Also, I guess the answers would differ depending on the language, so I'm looking for information related to the English/en-US versions only (I believe there is an en-GB version as well?)
The Windows 8 Upgrade Assistant allows one to create USB/DVD (ISO) media:
Is the media customised per-PC in any way, or are copies created on different PCs with different base OSes (XP/Vista/7) exactly the same?
If the ISOs are not customised, are they exactly the same content-wise as the Upgrade DVDs available for purchase?