When the incentive to prosecute (i.e opportunity for resources gained vs opportunity for resources lost) reaches a certain thresh-hold there's action. Generally, that thresh-hold is high because the value gained from prosecution is low, even in cases were one party is quite apparently guilty.

The only real exception would be the "let's make an example of out this person" case. When crime is rampant, prosecutions might happen with greater likelyhood in order to deter more crime for occuring. An example would be pirating music. It is not feasible to prosecute people for pirating music, but suing 1 party publicly will get 1000s of people to stop instantly.

In this case, the add-click businesses engaged in fraud. So was it fraud to trick them?

The point is somewhere well beyond a fifteen-year-old anecdote told anonymously in a public forum.

Certain companies deserve it?