Just a theory but I could see big players wanting to down the 'retail' exchanges, big money doesn't want retail traffic interfering with thier big plays.
All sorts of speculation is going through the market right now. Some people even say that certain exchanges have a market limiter in place, that halts trading at the time there is too much volatility.
I rather stick to a surge in traffic as being the main reason. People see a massive dump happening, and based on that desperately look to buy the dump, or panic sell to prevent potential further losses.
Poloniex, Wex (formerly known as BTC-e), Bittrex, and a few related exchexchanges, have had this even with slight traffic increases, where they recently have performed rather stable, which is something unexpected.
In these cases you would expect the top Bitcoin exchanges to remain stable, but it's completely the opposite, lol.
