AppleScript Importer imports source and description from AppleScript .scpt and .scptd files into Spotlight. The AppleScript importer will only work for .scptd files if it is installed in "/Applications/AppleScript/Script Editor/Contents/Library/Spotlight". It will not import .scptd files if it is installed in "/Library/Spotlight" or "~/Library/Spotlight" (although it will import .scpt files). If you want the dirty details, please look at the AppleScript Importer ReadMe. Hopefully this restriction will be removed in a future version of Mac OS.
Mac OS X 10.4 or later