Good question, this is what i think. A lot of the famous pianists have either their mother or father teaching piano or playing piano, therefore, if they have a gift it is soon noticed and nurtchered every day, secondly to have music around you every day is an important factor, thirdly his or her parents will have the necessary knowledge to help that child to perform in public as soon as possible, this is the main advantage they have over most people, however their are exceptions to the rule.