The reason why member reviews are weighted more is because they are more accountable. Guest votes are only tracked by IP and time, so unless your the RIAA you won't be able to question that person again about their vote. With member votes a confirmed email address is recorded (As they had to have it to sign up). This is good because if the review's validity is questioned, it's possible to go back to the review's source. Without this it would be impossible to determine if the review was bogus, placed by a competitor of yours, or any other of the number of reasons a review could be questioned.
Now for your second part, I know the ability to respond directly on the site to the reviews is/was planned, just not completed as of yet (or if it is they haven't released it yet). If you have a serious objection to any review listed on the site I would suggest you use the helpdesk link at the bottom of any page of Hotscripts (
http://www.hotscripts.com/helpdesk/index.php). I am more than sure the site owners would be happy to assist you in anyway they can.