You just don't get it. It's not about centralized / decentralized bs...it's about liquidity. How do you bring thousands of traders face to face IN THE SAME TIME 
?
If trader X place a market order on a site and that order is not executed in the next 30 seconds (like on MtGox ), trader X WILL LIVE the new exchange in 5 to 15 minutes. And he/she will never come back again !!!
Ask yourselves : Why do we have only 2-3 big exchanges The answer is : LIQUIDITY !!! It's the most important aspect of an exchange. Tens of small exchanges died before launch because of this problem. It's almost impossible to have 1000 buyers and 1000 sellers in the same time, on a newly launched exchange site. Period.
? If trader X place a market order on a site and that order is not executed in the next 30 seconds (like on MtGox ), trader X WILL LIVE the new exchange in 5 to 15 minutes. And he/she will never come back again !!!
Ask yourselves : Why do we have only 2-3 big exchanges
The answer is : LIQUIDITY !!! It's the most important aspect of an exchange. Tens of small exchanges died before launch because of this problem. It's almost impossible to have 1000 buyers and 1000 sellers in the same time, on a newly launched exchange site. Period.