The links on the page k3tg supplied have more links which explain the rating process. The actual parameters they use I am sure are a confidential process. Often a ratiing may appear to be illogical to you the user but you have to remember that this is largely an automated process and it takes a while for a website to be reviewed and then re-reviewed and things can change in between the two.
There is a link there on how to contact SiteAdvisor if you wish to ask them directly.
Message was edited by: Ex_Brit on 28/05/10 9:50:05 EDT AM