Basically if they let it go to zero, then you can bet someone was running a money tree on the way down, I mean, traders LIVE for arb positions like this. It'd be worth bribing a Gox employee to get a window at these spreads. I mean, frankly, Gox should halt trading if they want to have any credibility.
edit
This is not some legal fiat market based arbitrage window, this is all crypto-lightspeed money transfer. The inducement to crime here is phenomenal, its irresponsible to law abiding BTC holders. Gox should halt if they drop below 100 otherwise its a shark orgy on the way down and SOMEONE knows how to get coins out as it drops, some .001% will have the exit, and they will make bank, flee, and that'll be that.
I totally agree, a HALT should have occurred long before now.