A major EX temporarily going down creates an increase of Buyers and a Decrease of sellers on all the other smaller EXs.

Normally this would move the price of bitcoins UP.

But it moves it down because all the market manipulators who run the prices up with small incremental buy orders (to take advantage of naive buyers who don't take volume into consideration) mostly live on MtGox. And without them the real supply meets the real demand.

"Panic selling"? Who would "panic sell" because their EX is going to be shut down for a day? And how exactly are those panic sellers going to verify, and set up accounts on the other EXs in that time-frame, and be able to then transfer their coins in time to those EXs - to "panic sell"?