This is what is confusing to me. It seems that 'winning' does not really mean anything (at least to my understanding). As you have rightly observed, there are games in top 50 with less than 20 ratings. By the rules, they haven't 'won' but they were given a ranking. So technically, a game with even 10 ratings of an average of 3.2 would outperform a game with 100 ratings with an average of 3.1 and get a better overall ranking :(