The reason Mac users "don't get viruses" is because noone has made any serious viruses for Mac, not because their virus protection is super-duper compared to Windows. If noone makes a virus, you won't get one!
People are starting to develop Mac malware now too, so watch out. There was a Mac trojan being distributed until not too long ago. And apparently some guy has developed a hack to all computers running on Intel chipsets, regardless of OS (in other words, that includes Mac). http://news.zdnet.co.uk/security/0,1000000189,39448046,00.htm