This is Microsoft's trick for blocking out other operating systems and also making sure that the motherboard has DRM-capability built-in so that they can can (eventually) control the users entertainment consumption. If the motherboard BIOS does not have UEFI-Secure boot capability, it will get rejected. But also, if the mobo does not have hardware that, along with UEFI, allows the OS to control ever aspect of the machine, it will get rejected. Microsoft is trying to turn the PC hardware industry into its own, personal hardware factory.