Sounds like a popularity contest to me, the ruy lopez and the italian are very popular compared to the bishops opening for example. If your statistic includes beginner games, then it's a self-fulfilling prophecy. Those who know to move the knights first will do so, those who dont, will play badly.
I assume you mean in 93.3% of all won games, the knights were moved first. Your statement suggests moving the knights before the bishops gives you a 93.3% chance of a win.
I have scoured my extensive chess databases and have come up with an interesting statistic you all might be interested in. 93.3% of all the games analyzed (nearly one million) were won where the KNIGHTS were developed BEFORE the BISHOPS. If you're a beginner, take this to heart. It may seem like a given to most people, but NEVER EVER EVER move a bishop until you first move a knight (in the opening).