Good artical, however I think the point is realtivly mute. It is true that currently OSX by default is less stupid then windows. However, I think it is truely the end user that decides how vulnerable a system is by what they do with that, OS independent, I could have a XP, OSX, and lets say Mandrake box, and they could all be equaly vulnerable depending on what I have done with them. With a straight base install, I would say windows would be at the bottom of the list, however, after you install a few firewalls on that box, put it behind a router(includes it's version of cheap firewall) it becaomes safer.
So, I don't think out of box security has much importance as whether or not the person using it does. If you browse less then reputable sites you will get attacked, and no mater how good your secruity is some will slip through. So the key is, don't connect your box to the NET :)