Motherboard change=new pc.

Did you know that if you change the motherboard in your pc then MS will see this as a new pc and you therefore need a new licence of xp? Apparently you can replace a motherboard under warrenty (but I assume this needs to be the exact same model) but how likely is it that someone could obtain the exact same motherboard 9-12 months after their original purchase?
I read about this on the partner website (I think) which implied that this was a new licence change, but the system builder chat in Feb2005 mentions this too - so it's not actually that new.