Changeing a motherboard has always severed an OEM Windows licence. This is why XP would not activate in the thread contained in your link. If you change the m/b and you use OEM XP, you must buy a new retail copy.
Or so I believed. During a recent conversation with Microsoft I was told that now both the m/b and the "chassis" whatever that is, need to be changed before the licence is severed. So which one is wrong?