2005's are coded to the car when fitted, don't try fitting it in another car though as it will lock it solid!
You can fit them in other cars, just enter the code. Its the NCDC 2013/2015's which are paired to the cars immobilisers and useless in other cars....
NCDC not paired to the immobiliser but generally uses the same security code 
Correct, its a bit of a hybrid system - whilst the later CAN stereos are indeed paired to the actual car itself, the NCXX stereos are simply paired to each of its own components, head, changer, telematics etc, all of which are paired together using the same pairing code from the original vehicle

Actualy, the later CAN bus setups arnt paried to the car either. I have done loads of testing for that on my mum bus with a CD30MP3 and CD70
They are paired to the Display, Bluetooth (if fitted), DAB (if fitted) and thats about it.
They do have the chassis number entered into them but, this can be changed with Tech2 easily (and is also a method for getting the security code from a friendly dealer !

) and none of the other body systems check this.