Its where the server is located that's the issue. I think those who get the 200+ Z a day are in Los Angeles and their ping is below 30. I'm in San Diego and my ping is close to 90. So they get to the server 3x faster. At least that's my working theory.I actually did some testing for mTurk.
I've been to the offices where they work on it. Yes, it's in Seattle.