Norton Internet Security 2011 for windows should scan for Apple Mac OS threats

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Norton Internet Security 2011 for Windows PC's should look for Apple Mac OS X threats while running a full scan.

But not only Mac OS X threats. NIS2011 should even look for Mac OS 9 and below(before OS X) threats and Linux threats(old and new)  Sophos AntiVirus for Windows does this, why doesn't Norton.