That data is stored with the game, and not in your collection folder once you submit it.
Thanks for your reply, Duke.Togo, but are you sure of that?
Take, for example, the European release of the PS2 game ".hack//Infection Part 1." Two members have submitted ratings for this and the average is 62.5%. But in the collection of member JHoningh the game has his (or her) personal rating of 65%. This value must be stored by the system somewhere. I guess another member has rated it 60% but I stopped looking after finding the game rated in JHoningh's collection.
In my case I mistakenly rated some games in my collection that I've not yet played and in an ideal world I'd like to remove my rating. The system allows me only to change my rating, not nullify it.
Like I say, not a big problem.