This site did a complete breakdown of the whole scam... seems to be similar to the fake domain name renewal notices where someone is sent an invoice as if they're an existing client. I'm only on page 2 of 3 but it's very interesting reading. I thought they were just annoying fuck spammers but it looks like it's a lot more crooked than that.
http://www.dynamoo.com/diary/topsites_topsitez_us.htm