The main difference is that anyone can create a practically untraceable address as many times as they want. So if you have a lot of tainted Bitcoin and you wan

The main difference is that anyone can create a practically untraceable address as many times as they want. So if you have a lot of tainted Bitcoin and you want to obscure the source without risking putting it through a mixer, you can create N addresses and start sending coin to (and through) them. Compared to checking accounts; I can't just generate a thousand checking accounts that don't belong to any identity and generate a transaction history that appears to show many transactions occurred between hundreds of parties. It's still not as good as mixing with other Bitcoin of alternate origin (if I only have the tainted coins at the beginning, I will still have 1000 accounts with only all of the same tainted coins when I am done, and a careful analysis will show that these 1000 addresses were funded entirely by the original tainted coins). But each seller cannot be expected to perform this careful analysis, and as you are able to exchange known tainted coins for clean coins and mix them, you can increase the uncertainty that a legitimate transaction is taking place that is separate from the one that originally generated your ownership of the tainted coins.