There is currently an insane disconnect between the price at Bitstamp and Mtgox. For most of the day the price different has been around $30, now it's about $7. A bunch of huge, completely irrational buys from some very unusual folks putting in big orders at a massively inflated price.
The buy difference at this point I think just represents more the fact that stamp follows gox so there is an apprehension about making a move before gox does it.