This isn't done on other exchanges. When buying/selling BTC, LTC, BTSX, etc. on BTER or other exchanges you aren't actually trading those coins. You're trading bterBTC, bterLTC, etc. Nothing hits the blockchain until you withdraw. I feel USD falls under the logic.
other exchanges issue IOUs for the currency itself. BTC, PPC, BTSX,
USD, CNY
X won't issue IOUs for USD itself, it'll be issuing IOUs for bitUSD.
I agree with the points being made here.