If we are to believe the order books, a lot more BTC and their fiat is trusted to MtGox than to BTC-E.
I think it is the other way around. Discrepancies are high for both due to difficulties getting fiat in or out. MtGox price, volume, depth and liquidity is higher because people trust MtGox more than they trust BTC-E.
Volume, depthe, and liquidity has little to do with price difference given that ARB opportunities would bring prices between two exchanges into a much more narrower range than they currently are.
Pretty sure some people or group are successfully arbing (maybe japan locals?), we keep seeing massive great BTC sell walls @ BTC-e to keep price down. Wouldn't be in this groups interest to spoil the large spread.
This is likely true. But my point is directed at the big money and not the small money. Obviously the big money is not local to Japan when speaking about arb Bitcoin price opportunities. Otherwise the gap would have closed by now. If there was a Japanese whale the gap would close much much faster. Free money is not going to be passed up.