What may be happening is more players cashing out of Gox via bitcoins. And arbitrage isn't working at all, even via JPY.
There is a small delay (possibly 1 - 2 days) in receiving bitcoins from Gox, so this means that Gox has to get bitcoins from cold storage.
This lead to a strange situation, where Gox looks bullish, while other exchanges do not.
I had ZERO delay in moving Bitcoin out of Gox. In fact moving Bitcoin out of Gox while I used it for two months was much faster than any other exchange.
So unless something has changed in the last week the lag should still be zero. I don't think Bitcoin withdrawal time has much at all to do with what we are observing. I think Gox users are sick of holding fiat and know they can't move it, so they are buying bitcoin and moving to cold storage or another exchange, like i did... a couple of weeks ago.
EDIT:
The bigger the gap grows the more desperate GOX buying will become. At least that is why I Bitcoined out of Fiat when I did.