It makes you wonder how many times virus writers have been contracted and failed to provide even a single working virus.
Virus writers were able to write viruses for Pre-OS X Macs. There weren't a whole lot of viruses (I never got one) but they were out there. But since OS X? It's been slim pickings. I don't believe for a second that the "lack of popularity" of the Mac platform has been the reason that it is pretty much virus-free. Lack of popularity certainly didn't protect Macs from viruses before OS X.