There are two ways to make inferences based on Rod Blagojevic's bribery case. Although they are not technically mutually exclusive they appear to me to be quite disctinct:
1) He is stupid. Because of his low intelligence level and his inability to project his actions onto future probability states, he committed mistakes that no rational actor with higher intelligence ever would have made. Evidence: Wikipedia says that he was a poor student (how much of an indicator that is, I don't know), and that when he attended Pepperdine Law School he didn't know where the library was. More incriminatory, when he was interviewed on The Daily Show in 2006 he did not realize that it was a comedy show!
2) He had access to inside information that the general public does not have access to. This information persuaded him that the risk of being caught are much lower than you or I would expect. Therefore his decision to sell senate seats may have held up to a rational a priori cost-benefit analysis. Evidence: We have no way of knowing how many public figures commit similarly illegal acts to Blagojevic without being caught. However, he would really have to be quite stupid for #1 to be true, and the fact that he was skilled enough to work his way to governer casts doubt that it is the full explanation.
I myself am not a conspiracy theorist, but I must admit that there is a nonzero probability of the second explanation being true. This kind of thing could happen all of the time without disclosure to the general public.