It's still a good old fashioned credit card setup but the local Hong Kong bank is the processor not an outside third party with multi-national locations giving OFAC leverage. As I understood it before this all started, Hong Kong's banking laws are very privacy minded. But World Pay has business dealings in many different countries so OFAC had an easier time asserting it's power. Whether they actually subpoenaed World Pay or simply asked for info, that I do not know.
Everyone assumed that Visa was a culprit in the first go round but it was really World Pay. Visa wouldn't have any idea where you make purchases without the 3rd party processor helping provide answers.
There's always the chance that Visa and/or MC could lean on a bank/processor to stop transactions with a vendor (of various things besides tobacco as well) that violate their rules. But they have a hard time doing so since A LOT of companies sell tobacco plus other items. And a company could be called "Acme Tools" and Visa would have no idea what kind of merchandise they sell. How can they say to Ravi's bank "stop processing his orders" when Wal-Mart sells cigarettes in store? In Ravi's case, his clients are all, at least legally, outside of Hong Kong proper. This means all of his business is either done via phone or internet. They can use the fall back position that CoH has no way to check ID. But they still have no idea whether a purchase was for cigars, humidors, whatever. And they'd be hard pressed to shut down a processor who handled his transactions solely on the basis of being a tobacco seller. Because then they'd probably have a stink raised by these guys to Visa over your Wal-Marts (that's why I brought them up earlier.)
This is really two issues: Visa/MC trying to prevent tobacco purchases from being made on-line by minors (which has to be a tiny, tiny amount of money) and OFAC trying to crack down.
In both cases, neither entity really has a way to tell what was purchased unless the vendor or client turns over transaction records. Which so far, from the vendor side, has not happened.