The only problem I see with Brett's sample is that we don't have any way of knowing how many (or few) people in his area have Norton on their computers.
I know you run Norton, Brett. But your success could be more due to your internet IQ than your AV.
And if less than 10% of your area uses Norton, you would necessarily get lower numbers of infected PC's in your shop.
It's like a mechanic saying "Buy a Maserati because I never see broken one's in my shop and I drive a Maserati."
It could be because Maserati's are dependable, and it could also be because few people own them.
I use an AV that's provided by my ISP, as well as MWB.