this isn't ignorance - Mac has a small enough market share it seems it simply isn't worth developing malware for it.
the problem with Mac OS X is that users habitually enter their username and password at "administrator permission" dialog boxes. It probably wouldn't be that hard to make malware that installed and propagated itself around networks. (bonjour, apple script and all the network toys Mac OS X installs..)
I think that if malware ever hits Mac it could be rather damaging.
