It seems that the OSX installers/updaters have zero tolerance for mucking about with the sacrosanct location of the Application folder. I've also noticed that various OSX installers bring back dead wallpapers, or disable them on a whim. I installed a tazl-inside desktop picture back on 10.0.0, and all the updates inbetween (that's right, I've never re-installed/formatted since 10.0.0) seem to do something different with it.
Still, you should see what happens when you try to upgrade from NT4 to Windows 2000 sometime... ::shudder::