This is an area where it's really hard to extrapolate from my personal experience to the entire population, but is this really an accurate statement of many people's beliefs?
I think what people actually think is that the chances are much lower of encountering malware in the wild on a Mac. In support of that, having an article this long on a single piece of malware that isn't particularly damaging, would indicate that it's not the normal state of affairs in Mac land.
I would similarly expect that the chances of drive-by malware on Linux are tiny, perhaps even less common than on a Mac, and thus it would be newsworthy if there were some widespread (in relative terms) Gnome malware, or similar.
It's one thing to think that it's uncommon, and another to think that it's impossible.