1) Adblock is quite simple solution, and advertising networks create new and new defence systems for ads. For example Google if you logged in, crypts traffic and sends it through https.
2) Not really. I don't know statistics in USA, but for example in Russia up to 80% of banner clicks come from only 2% of heavy-clicking users. And about 10% just completly ignore them, or use adblock to hide banners. It's just a way to monetize this kind of people.
3)It doesn't really work like that. People buy it usually after 14 days of trial, so they either like it or not. A large number of our affiliates just distribute their unique installers without sending ppl to our website.