I think it actualy goes by IP addresses when voting.
Here are their rules:
Every Top 100 Sportbike Site member wants to be Number 1 (or at least in the top 10). The best advise I can give is to place your voting button where everyone can see it. As your site grows in popularity, so will the number of votes you receive. Superbike Club reserves the right to suspend or cancel any member's account who is caught cheating to raise there vote count. This includes automatic voting programs installed on your site, multiple votes from the same IP address in a short period of time (including the use of IP address changing websites), and "tricking" visitors to vote for you (ie: placing a link on your site that says one thing, but gives you a vote on the Top 100 list instead).