"For laymen's purposes it pretty much is, though. When was the last time anyone on Linux/OSX got some adware / popups?"
For OS X, one or two months ago. Do a web search, the times are changing for Mac security.
"I've also never heard of antivirus for Linux. Which doesn't mean there aren't viruses, it means it's not a concern on the most part."
No, it just means it's not your concern. When online crime has become a business, it makes sense to try to protect yourself. Major AV companies have a product for Linux.
For OS X, one or two months ago. Do a web search, the times are changing for Mac security.
"I've also never heard of antivirus for Linux. Which doesn't mean there aren't viruses, it means it's not a concern on the most part."
No, it just means it's not your concern. When online crime has become a business, it makes sense to try to protect yourself. Major AV companies have a product for Linux.