I Guess you will only see that if they advertise, because I'm sure they would mention it to ally fears of buying a system with XP and then having to fork out again to upgrade to Vista.
If they have the same offer they will sing it to the heavens to compete with those who will be making a big deal about it, 'don't delay buy today, free Vista Upgrade,' etc. etc. However, knowing MS it will be the volume buyers who have the clout to demand this special treatment.