Why do some people have a lot of unexchanged coins, and why do some people have not? I did have a lot of them, but they are exchanged.
My guess is that it depends on which coin he/she has been mining. As noted by h20, the EU server is mining doge only and I'm guessing there's autotrading setup for that coin. For users on the US server though, more "exotic" coins are being mined and in those cases, the trading is done manually and less frequently.