Ha Ha, That didn't even cross my mind, but of course you're right.
Good to know there are people more awaik than me,
While a win8.1 download contains a install.esd file windows 10 has a install.wim file....
on the windows 10 install.wim i run this:
Dism /Export-Image /SourceImageFile:install.esd /SourceIndex:1 /DestinationImageFile:install.wim /compress:maximum
the file goes from 2.0 to 2,4GB (for the 32bit)
Just to let you know both 8.1 and 10 eats the produced wim named esd file without problems and it seams MS is making esd files renamed as wim files also....
my windows 10 64bit install.wim(esd) is already 3,5gb (containing 10,pro,enterprise & education)
I predict that if I exported them using /compress:maximum, I will bust the 4GB limit, breaking Fat32 support for my usb stick install.