It appears that ARM devices can fallover to legacy BIOS mode to support non UEFI OS's.

From page 109 of windows8-hardware-cert-requirements-system.pdf:

  System.Fundamentals.Firmware.UEFIDefaultBoot 

  Target Feature: System.Fundamentals.Firmware 

  Title:  All client systems must be able to boot into UEFI
   boot mode and attempt to boot into this 
   mode by default 

  Applicable OS Versions: 
    Windows 8 Client x86 
    Windows 8 Client x64 
    Windows 8 Client ARM 
    Windows 8 Server x64 
    Windows Server 2008 Release 2 x64 

  Description: 
  The System firmware must be able to achieve UEFI mode
  boot by default. Such a system may also 
  support fallback to legacy BIOS mode boot for deploying 
  OS images which do not support UEFI, if the 
  user explicitly selects that option in the pre-boot UEFI BIOS menu. 
  This requirement is If Implemented for Server systems and applies
   only if a Server system is UEFI capable.