Noticed in this thread
https://bitcointalk.org/index.php?topic=162758.0 that someone mentioned the Mt.Gox waiting list was 8000+
Doing some quick math, if we assume on average that each new account will purchase 250USD of Btc, (a number I just made up, but follow my reasoning here) then that is 8000x250USD= 2,000,000USD. Looking at the trading depth on the ask side, even at an average price of 110USD/Btc that money could purchase over 18,000Btc.
This more of a thought than a calculation, but my point is that the average holder of coins probably doesn't want to sell in the short term.
Peace