I would imagine the number of accounts that have actually been sold since Silk Road's inception to be in or around the 15-25 region. It is not an issue of money. It is most likely that DPR allows this because a) it is impossible to prevent, due to the fact that we are all accessing Silk Road via Tor and b) because restricting the one item that he/she "sells" (used loosely as the payment is a bond, not a fee) on the free market that he/she created would be crassly hypocritical. Libertas