Sounds pretty easy to connect the dots to me...
So now the hacker has 10BTC in the mixer, he requests to be paid out to a list of 20 addresses. These addresses are sent between 0.1 and 0.9btc until the mixer has sent out 9 BTC (taking a 10% commission for the service).
None of those hacker controlled addresses have any connection with one another and they have zero connection to the original deposits made by the hacker.
There are also another 10 hackers doing exactly the same thing, so now we are looking at hundreds of transactions. So it becomes very difficult to connect the dots, also if you really could connect the dots easily I imagine that the FBI et al would really like to speak to you.
Money laundering is disguising the origin in general, which is of course the point of mixing. It's not some kind of theoretical bitcoin boner exercise, it's intended so you can maybe at a later date withdraw some bitcoins without the party providing the cash (and the feds) immediately making the connection to the crime.
Bitcoin mixing disguises the origin only as far as the blockchain is concerned, you still end up with X BTC that you have no explanation for how you earned them.
Still obfuscating the source of funds or making it harder to trace is what both Money Laundering and Privacy are about.
Sadly, politicians don't make it easy to be 'almost private' (to everyone but the government it's a secret).
Transactions on the Bitcoin blockchain are public, so it's relatively easy to keep tabs on movements of known criminal proceeds (as the article demonstrates :)
Until they've been obfuscated by a mixer... and not every mixer is going to be interested in blacklisting every set of coin from every known criminal activity. And many criminal activities are surely unknown, including many for which the sources of coins are not going to go to any extent to report. (The senders may be committing crimes that were unrelated to Bitcoin crime, and so entirely off the radar.)
I'd hazard a guess that the majority of crime committed in and around the ecosystem of Bitcoin is not even Bitcoin theft, so might never be reported.
How many times does a value have to move from one address to another address, and mix with untainted coin, before it's going to be considered too far removed from the original addresses to be palpably associated with the original crime?