The key are all coded - the reason to match the purchase to your bike is so the the physical bumps and ridges in the slot match up to the mechanical security of the lock (for your ignition and luggage locks)
The coding itself does as far as I know need a visit to the dealer as that is random and not specific to the bike you own - until the linking to the bike is done anyway.
When I bought my GS, the dealer included a plastic slimline "wallet" key as well as the 2 standard keys. The wallet key is an emergency item to carry just in case you lose the main key so does contain a coding chip but would wear out if used every day. Not sure off hand how many keys can be coded to a single GS, but it is at least 3.
Oh and if you lose a key you go to the dealer with all your remaining keys and they remove the lost key from the security of the bike so that it can no longer be used to start the bike (which again shows that the keys have different codes)