I think it's relevent to suggest that most Linux users would be more technically proficient than the average Windows punter, and therefore would be more likely to have security measures in place. Of the 92% in that article who claim to have never had a virus while using Linux, I wonder what percentage of those would never have had a virus using Windows either? Probably quite high, I would guess.
I also think it's highly prpbably that virus writers don't tend to target Linux, because of it's low ratio of users, much as they target Mozilla / Firefox much less than Internet Explorer, but if a higher ratio of users switched to Linux, they would soon start to be targetted more frequently.