Words Of Wisdom on 18 March 2009
Most ad sponsors typically pay attention to hits and click-throughs (terminology may vary).
An ad gets a hit when you see it. An ad gets a click-through when you click on it. Some ad sponsors can even link click-throughs to purchases. Based on those factors, they either usually pay a certain amount of money per factor (per hit, per click) or buy ad space for a fixed amount.
I have no idea what the deal specifics are on vgChartz but that's how, in general, internet ads work.
