Unsubscribes only seem to work for UK companies as it has been legislated for. I suspect that most US (and other) companies just add your email address to their "Sell it to spammers" list. I bought some clothes from a US retailer whilst over there using a one-shot email account I'd setup for that purpose, and they proceeded to send me marketing emails every single day. I unsubscribed and it took 2 weeks for their marketing emails to stop. Shortly after that the account started getting all kinds of willy-pill and get-rich-quick spam. No biggie, I just deleted the account, but really shitty business practice and they have lost me as a repeat customer.