It would actually be preferable to re-balance using Bitcoin since the fees involved are generally much lower.
I'm sure it has not escaped you that if you want BTC, you need $$$. Waiting for an opportune time to convert BTC to USD for the purpose of having USD to buy BTC takes more time, skill, and luck than a lot of us have.
In any case, this is an interesting development. Up to now TradeHill and Gox have been fairly efficiently arbitraged with few exceptions. What seems to be happening is that someone has a large Bitcoin position to liquidate but if they were to sell 11,000 BTC on Gox it would cause a rapid drop in price. So they are taking advantage of the friction between the two exchanges to optimize the rate at which their position is sold, so as not to crash the price. This becomes more of a concern when the price is already low because there is less market depth to absorb the sale.
I'll defer to your expertise here. Your hypothesis sounds more realistic than mine.
Another fun hypothesis is that it is a plot by Tradehill to get some user's to take the plunge and get around to setting up and using a Tradehill account. That might be a good investment for Tradehill actually.
I am fine with this, it will have the net effect of driving volume to TradeHill, which I would like to see better balanced with Gox. And it will force more people to trade on both exchanges if they want to keep their volume up. It certainly complicates money management a bit, but it is actually safer IMO to be better diversified in this way.
I agree very much, and it was a big factor in my primary use of Tradehill. Even Kenna has at least paid lip service to this philosophy in the past (which is easy enough to do when you are trailing by an order of magnitude I suppose.) I would like to see several healthy and trusted exchanges in every major locale (Eurasia, Eastasia, and Oceana for lack of a better delineation.) Maybe a franchise of highly autonomous exchange outlets could be viable to instill some confidence and provide some level of back-end support, but not until the economy grows by several orders of magnitude.
But back to today, one could still loose all their chips in some domino effect which took down what few viable exchanges exist, but one should at least be somewhat insulated from garden variety coding fuckups or the types of corp/gov exchange harassment which seems endemic and unlikely to subside.