I actually don't think the stars have anything to do with ability at all. I could be wrong on this, but I think I read somewhere they are simply an indirect measure of how long you've been on the site and how frequently you play. They are tied through some formula to the amount of rake you have paid.... Longer on the site, higher volume player, ....more rake paid.....more stars earned.
This is also why you earn stars faster at ring games than SnGs and MTTs where you just pay one small fee and may play for hours depending on the length of the tournament, whereas with cash games they are constantly taking little chunks of rake from you. Also, if you'd rather remain anonymous, you can always elect to have your stars hidden.