There have been many average or below average PC users that have avoided viruses for a very long time. There are many people that can't avoid getting viruses. They should switch to OSX.
I think there is a large mis-understanding going around. OSX is not a more secure OS. Its a very very low priority target. Its not about how long an operating system has been out. It is about the amount of users and the amount of software. You can have an OS out for 100 years, be half as secure as windows.
There are way too many OSX users or fans that have very little knowledge on the subject, but can't help repeating that OSX is super secure because its based on an operating system they have very little knowledge of and windows is ridden with viruses no matter what you do. The simple fact is that if you know how to use a computer windows 7 will be fine. You will be more targeted. It is not less secure then OSX. I think most people, who know what they are talking about, would agree that OSX is actually less secure than windows 7. But, its very easy to target windows 7 due to the variety of software and amount users.