If you've installed the Apple Keyboard drivers with AppleKeyboardInstaller.exe (or AppleKeyboardInstaller64.exe) on a PC you'll quickly discover all the function keys are treated as special keys. To get the function keys working normally as you'd expect, it's controlled by a registry key:
[HKEY_CURRENT_USERSoftwareApple Inc.Apple Keyboard Support] "OSXFnBehavior"=dword:00000000 "FirstTimeRun"=dword:00000000
0 = Use function keys 1 = Treat as special keys