its that simple there will always be some trace of drugs on a BTC like the dollar 99% has coke traces on them.
BTC-E iss offshore and are exemped of this.
further it does not realy matter bitstamp is NOT a US exchage bitpay is now controled from amsterdam so.....
Tacing back bitcoins wil be harder an harder if not imposible.
because all bitcoins by now could be touched one point in tine by adresees that where once connected to silkroad
and yuou cant replace bitcoins by new one's
so this way of checking will get them to notting.
but knowing this HSBC is respsible for wassching BILOINS of dollars.
it will drive out the bitcoin comony's away to places that do not care.
like thailand
http://www.coindesk.com/thailand-bitcoin-exchange-reopens-enhanced-services/or btc-e