- Why would the spread close in June, even though there were no verification of Gox processing withdraws again?
Recall that June was only a little bit after timely withdrawls began to be a problem, and at the time, Gox issued a statement implying that things would be back to normal on the 4th of July. It's possible that some folks with deep pockets, speculating that everything was about to return to normal, decided to conduct arbitrage prior to actually being able to withdraw their money.
Why wouldn't the spread be closer to 1% if gox was arbitraging?
If such a scheme is going on, a consistent tight spread over months would give it away. Sooner or later speculative arbitrage will run out of money, which means the only way to keep the prices equal is a back-channel. Keeping it at 10% or so, in this hypothetical, better matches people's assumptions and gives them less reason to reevaluate.
- There's probably a limited amount they are willing or able to trade at any given time. Any other exchange can freeze gox's accounts, ban them, or whatnot if suspected they were doing this.
Why would any exchange in their right mind do that? If Gox wants to set up arbitrage to Bitstamp, for example, it's no skin off their nose. On the contrary - it would line Bitstamp's pockets with trade commissions and increase their volume. If Gox is doing this sort of trick, it's in the destination exchange's interest to
let it continue. I'm not even convinced that it's unethical - Bitfinex does a similar thing, by "routing" trades to Bitstamp when they're better than the local ones.
