Kirk wrote: If one is going to pay the price premium for Apple's walled garden, why the hell go outside it? Buy an Android and study up.
Yeah, the only way to "infect" a Mac, is still to prey on... those who don't know better, and trick them into installing something. Technically not "computer viruses".
BUT, there's legitimate apps outside the mac app store, and if you need older apps, they're not there either. Aaannd... then there's piracy.
But yeah, stay inside the mac app store and you should be fine.
By the way, as far as I know, staying inside the google store should be safe for android. Sometimes bad apps get in there but google usually removes them within days. And (but) there are antivirus apps for android (for a reason).