Well, they're right, partially. A lot of the PC community has the stance that they just don't care about Macs, and it's a big part of the reason we don't get viruses. The people that write the damn things just never need to infect Macs, because not enough people use the things for them to matter.
Yes, it's true it's harder to write them for Macs, but it's not impossible, and if Macs were popular enough I have no doubt there would be a plethora of viruses for the Mac. That's still to our advantage, though. A company switching won't really see viruses as much of a threat to their new Macs, not at first. But once everyone is using them... well, then it'd be a concern.
I always thought those ads were arrogant and condescending. The Mac community will always be seen that way if we always act smug when confronted with our own faults. Ctrl+Alt+Del is brilliant comic, and it's a gaming comic. It's right that they don't care, because we're hardly gamer friendly. If you don't like what they said about the ads, don't search for Apple in the archives... won't be to your liking. :/