Rav Lazer Yudel Finkel is known for pointing this out. When asked why the Americans learn as well if not better than the Israelis once they get to Bais Medrash, he responded that the Israelis never played when they were young, so they make it up when they get older. The Americans played when they were younger, so they are refreshed and able to learn when they are older.
I believe it was Rav Nossan Tzvi. Sorry about that.