Ok now post a link to a virus that attacked the OS and not an application.
Nevermind I see where you mentioned the Mac was attacked.
So do you see what is in common amongst all those? They were self-replicating viruses. In today’s world that is less and less likely (at least at the OS level). But malware is more and more common and it requires tricking users (typically) or getting them to visit a site.
We are mainly talking about malware and you come up with a virus. I guess by your definition windows 7 is rock solid since it hasn’t been attacked with a virus as you described and it has a larger install base.
Irrelevant. The issue is whether a small install base of software (an OS is software) will prevent malware writers from taking interest in and exploiting that software. If they'll look at 12,000 ISS products and say "I'm going to take the time and effort to write malware for this," they're definitely going to do the same for 50+ million installs of OS X. And they have. They just haven't been very successful.
And keep those goalposts moving!