Hi iPiplu and Bob,
This must be a new standard as I have 10 items register which include last years model of the "Airport Extreme and Express", Nano, etc.. I purchased the new 2013 Airport Time Capsule (2TB) over the weekend and read the prompt stating this serial number was an 'Accessory'...hence unable to registered. Right O, already filed the reciept! It was nice though to have one place to look at all your Apple products and confirm warranty status, etc..