Dell KB212-B USB 104 Quiet Key Keyboard, English, Windows® 8

Hi - I just purchased a new Dell OptiPlex just a week before Windows 8 came out and have upgraded to Windows 8. 

I notice on the Dell product page for Dell OptiPlex 9010 that the keyboard Dell KB212-B is not compatible with Windows 8 and that a new Dell KB212-B + Windows option is available. 

What is the difference?   Why is one not compatible while the other is?