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.
I think Bitstamp is looking more at what China is doing. Gox went down from 350 to 330 just now and Bitstamp didn't even move an inch. Only when China dropped a bit someone decided to dump a few coins on Bitstamp.
Exactly, I also noticed this behaviour for some time.
gox and btce follow each other
china and bitstamp follow each other