I agree there is a risk no matter what, but statistically the risk is much lower with OSX.
Hackers are like advertisers, they want to get as much bang for their buck as they can. Statistically, you're more likely to see higher quality/bigger name advertisements during primetime/big sporting events on major networks... Why? Because advertisers know they will get the most exposure where the most people are tuning in. The same goes for PC viruses. If the Apple market were ever to grow larger than the PC market , I suspect you'd see an explosion of Mac viruses and innovative new ways to plant them.