If you pick the DIY option, you can omit the Windows license. You'll have to install Linux yourself, but that doesn't seem like a terribly difficult task for someone already going with the DIY option.
I'm guessing they don't want to officially support any specific distro, and offering support for multiple distros is probably a bit outside their wheelhouse at the moment. [e: this is perhaps not the case]
I'm guessing they don't want to officially support any specific distro, and offering support for multiple distros is probably a bit outside their wheelhouse at the moment. [e: this is perhaps not the case]