Most of these sorts of sites work via pyramid scheme like you stated earlier. Some just get their payouts by now having the ability to send you advertiser (third party) e-mails that are loaded with crap you don't want. So long as they have a certain number of e-mails going out, this satisfies their sponsor requirements. Whether you actually buy something from these e-mails or not. Be careful as they may send out your personal information to other companies as well.