Responding to you specifically -- I forget that some folks don't know about these. Bitcoinwisdom.com ... a few minutes playing with the graphs and all their monitored exchanges and you'll probably be able to understand the patterns just fine yourself, if you know the basic differences in the exchanges' operational methods. Without seeing it, I guess it is kinda confusing why there would be a difference. Watching the marked in action will clarify it for you.
I love that site. I'd be much poorer without it. I gladly pay the ~$10 or whatever per month to keep their servers ticking without hiccup. I have a dozen screens throughout the house, and while some repeat, that's a lot of simultaneous connections. Can't say enough about bitcoinwisdom...