The rating system is working as designed.
I submit to you that Boxxi, who is a wizop here, has a skin that is being debated and "only" has 2.5 stars is proof that there is no bias involved. Even guys like me and Boxxi, who are high access people and have been here since the beginning, regularly put out skins that are rated as average (2.5 stars).
It is also getting a bit annoying, after having been corrected, that some people persist in claiming that WindowBlinds skins require a 3.5 star rating to be seen by anonymous users. This is false and demonstratably false (just log out and look for crying out loud).
There will always be people unhappy with the rating system. And if we did away with it and made for a warm fuzzy happy fluffy site where everything was 5 stars and shown to the world, then people wouls stop coming here because they would be unable to sift through the poor quality content.
Your options are: Either harsh moderation where we outright reject content that we think is not of the highest quality or a rating system where users who have earned the right through contributing to WinCustomize in one form or other give their views on skins and themes.