vendors account for the bulk of the stolen coins. Apparently the site made some feeble excuse and ceased vendor withdrawals for a week. That is a lot of escrow build up. Some social engineering with a trusted vendor or two kept things from going pear shaped too fast, and then they made off with all the escrow when the jig was up.
Before people say well it is a problem peculiar to pathetic junkies, the same thing could happen to anything in the BTC world that is very popular: An E-commerce site, a tumbler, e-wallet service, btc exchange, you name it. With sufficient incentive (a lot of btc in transit and a spike in price) the same thing could happen either on purpose or opportunistic or a hack, of course.
True it could happen to anything, but it happens more often for businesses that are illegal themselves. You have a tough time going to the police and saying, "I'm a drug dealer and was scammed out of my drug money!"
I wouldn't be surprised if maybe this was some sort of a sting operation as well. The government would be smart to pull off stunts like this so as to completely destroy the faith of users in online "black marketplaces".
