OEM license is tied to the motherboard it was first activated /installed on, if you change your board then a new license is required - this has always been the same for OEM versions on XP, Vista and Windows 7, Retail versions allow you to change license between motherboards / systems belongs you uninstall it form the previous version.
Windows 8 is slightly different as they don't have a retail version and the OEMlicense can changed between boards.