Reinstalling XP when upgrading MB/CPU

MS and MS MVPs say to reinstall XP when upgrading a MB/CPU:;en-us;824125

However, I've never had to reinstall XP after upgrading a mobo/CPU. XP
has always found and installed the new hardware. When I told the MVPs
that they said I was "very lucky." What's the deal?
"Your estimated wait time is 8 minutes; your actual wait time may
vary." Microsoft tech support