Couldn't you run some kind of scam with a program that justs keeps refreshing pages and clicking on links? Even if it only counts unique IP's I'm sure there's a way around that.
that's why the system doesn't rely on views alone. Some systems go as far as to only count the clicks that result in purchases.
Oh and if you are suspected of cheating your ad account is gone in an instant. along with all the money you've "gathered" so far. (Most systems only pay you after you've reached a certain sum). If you think you are helping by clicking an ad on page you want to support make sure you don't click it too many times.
I'm sure someone can find a way to cheat here too, but it cheaters can be very easy to spot as most of them tend to be too greedy. One idea would be to use all that spyware to generate clicks from all those infected computers.