MtGox is basically the largest exchange. It's bigger than all the other exchanges put together and accounts for some absurdly high percentage of all BTC currency conversions.
...
On must assume that Mt. Gox cooperates fully with any government investigative body (whether it is the case or not.)
It is also rational to believe that a relatively high amount of activity surrounding the use of Bitcoin involves people who are involved in activity which is of interest to various governmental investigative bodies.
As evidenced by how many people get scammed, it can also be noted that a fair fraction of the users of Bitcoin lack the knowledge or basic native intelligence to utilize Bitcoin in a truly anonymous way no matter what they might be using it for.
These things taken together (with the observation in the OP) give the Bitcoin system and ecosystem the potential, at least, to be a truly remarkable honey-pot. I often wonder if this is some of the reason Bitcoin has gone on as long as it has without being terribly molested by law enforcement. Indeed, some of the members of the U.S. legislature who were once vocal in opposition to Bitcoin seemed to have clammed up and even more interestingly it seemed that for a good portion of the previous year a lot of the mainstream coverage of Bitcoin was surprisingly positive...in my reading of it at least.
