This was initially going to be in the first version of Bitcoin Block Explorer, but I decided that it would have no real use for detecting "dirty" coins. The scammer would just send all of the coins to MtGox or something and withdraw clean coins. Only innocent people would be hurt unless the scammer is really stupid.
I rather not give the scammers that much credit - but yeah you do have a good point, and it's what I like about bitcoins to begin with; just a shame for all of this to be going on when bitcoins are receiving proper media coverage.