I can think of two possibilities:
1) Compatibility mode may have been written by Microsoft only to deal with programs written for Windows Vista or before, thereby not having a Windows 7 compatibility mode option. In this case, although the rest of the discussion board points to its imprudence, the logic goes that Windows 7 programs should "just work" on Windows 8. Regardless, I am pretty sure that compatibility mode is not really designed for use with drivers, but rather for use with other programs. Drivers are a basic system level code implementation of device calls made by the OS. In your case, it's the translation from Windowsese to the device's base language. Regular programs make OS calls in a particular OS version's dialect for device resources. In your case, this would be requests in one Windows dialect for device resources that only need the translation to the Windows 8 dialect before the translation to the device occurs.
2) The underlying version of boot camp you happen to be running was written to work with Windows XP and Windows Vista. Seeing an unknown version of Windows, from the perspective of the boot camp program, the error handler may be using the Windows XP drivers with the thought that the version of Windows you are using is pre-Windows XP (the only alternative case at the time that version of boot camp was written). If you upgraded to a more recent version of boot camp where Windows 7 is the only version of Windows to deal with, the default boot camp drivers, according to the previous logic, should be Windows 7 drivers. If you do upgrade, it would be prudent to make certain you have a full version of Windows 7 or Windows 8 to go on. If you upgraded from Windows XP or Windows Vista, upgrading boot camp right now might not be a wise choice.
Ultimately, whichever possibility happens to be the case here, Mende1 is correct in saying you should wait for drivers from Apple written explicitly for Windows 8. Plenty of driver problems have been plaguing most users who have upgraded, even with Windows 7 drivers. It may be 2.5 months (January 22nd or 23rd) before Apple releases said update, assuming it take Apple 89 days from Windows release to update boot camp as it did for Windows 7.
