They're using a loophole... they're not selling you content, they're selling a Membership. If you go to the CCBill payment screen and choose the billing option dropdown, you will see... you are buying a 3 day non-rebilled membership. Nor are you getting any kind of "product" in the mail.... you download the stuff as opposed to getting a disk. So essentially, you're buying a 3 day membership to download access to any given set.
I guess that works... but it's not the right way to do things, and I can imagine it's ugly on the paperwork end for both parties.