To be fair, their slogan is currently "Macs don't get PC viruses" . Which is true. Although, devilishly close enough to blur the two in somebody's mind.
1. "A Mac is susceptible to viruses. But it is not susceptible to viruses plaguing Windows-based computers."
2. "A Mac isn’t susceptible to viruses, whereas a Windows-based computer is susceptible to thousands of viruses."
The fact that you still get viruses, but they just don't happen to be the same viruses, isn't worth stating. So as a customer, it is very unlikely that I would infer the former (Meaning 1) from the statement. Yet it is what is meant.
I would personally call this misleading (and dangerously close to lying).
They are implying that viruses are a severe problem on PCs that Mac users do not face. This was undoubtedly true when they were running those adverts.
They're saying PCs get viruses and Macs don't because of the way it's designed. Not that PCs get PC viruses and Macs get Mac viruses.
They are also implying that it's the sole reason for the lack of viruses, when it's mainly the lack of users. That would explain why it's not susceptible to every other type of software available on Windows.
I guess they should be "thanking" the general incompatibility with Windows binaries.
I know I'm playing semantic games here, but so is Apple with this slogan :)
I had a long time Apple user ask me if I had a Mac or PC. I was using Ubuntu Linux at the time, so I said PC :P
The term "PC" persists not just for historical reasons, but because its hard to come up with a replacement term. A "Mac" refers both to hardware and the OS, whereas a "PC" means "Windows OS running on Windows-compatible computer". I suppose we could replace the term "PC" with "WOS-ROWCC".