No, you are right. I did 2 system upgrades in the last year that involved a new motherboard, and both times I had to re-authorize Windows XP. The first time, I had to call because it wouldn't authorize online. It's effing ridiculous because the whole time I've had 2 systems and 2 purchased copies of WinXP. M$ is going to be even more unpopular for making people spend another $100 every time their MB craps out, after the first time...
I seriously doubt there's any way you'd have to re-register your windows if you had to replace your motherboard. atomdevil is creating hype and must be refering to a motherboard upgrade or system overhaul.