It is hard to know what is what. The size of transactions is not a good indicator of criminal activity. Every day, entities move what looks like an astounding amount of money but it's just a drop in the bucket compared to what financial institutions move around. The big transactions are casinos, hosted wallets and exchanges and they are often moved automatically to ensure security. Basically, in a public/private key system, you have to move your earned bitcoins from a wallet where the key is hosted on the server, to a wallet where the key has never touched the network (it's called a paper or offline wallet). So basically, the money is not necessarily moving from one entity to another but being stuffed under many mattresses owned by the same people :)