What if someone doesn't have any previous OSes they can install on a brand new hand built PC?
Would they have to buy the "system builder" version or something like that?

I wonder if it's possible to just stick in an old Vista DVD (I have a 32bit OEM Vista DVD and a OEM 64bit Win7 DVD)
Let it dump the files to the harddrive so I at least have a Windows folder on the drive
Stop the install
Put in the Win8 Pro DVD and do a custom clean install.
This way you don't have to go through the whole process of installing the entire old OS.