I'm quite amazed where these huge sellers get their coins from.
Remember those 850.000 bitcoins "lost" on the MtGox? Somebody has the private keys of those BTC. Ask yourself what would you do if that was you. Would you hold all of them, or would you convert some to the fiat?
I would be wary of exchanges. If you look at Stamp, for over a month, you see huge sell walls placed at intervals. And to withdraw that much of fiat, the exchange would require your identity and bank account. So, the key person to know why the huge btc quantity of sell limit order is the exchange owner.
Many people are speculating why the market has been so bearish. If the bitcoin news websites are smart, they would bug the exchange owners for answers. Think about it, all we can see are just the orders and transactions. The
exchange owners are able to see who are placing these orders and making these huge transactions.
For exchange owners to publicly reveal the identity of their customers would be a breach of TOS and probably illegal. Who would trust such an exchange? You can assume if somebody is dumping the MtGox "lost" coins he would have bigger worries than being doxed by the exchange.
If you analyse in which way you would dump some of the 850K (-200K) of MtGox coins if they would be yours, one can come to conclusion it would happen exactly as it happening now. Try to keep the price as stable as you can, don't bring it down more than you have to. Disperse over several exchanges. Drop more on the good news. Take your time to analyse the buying patterns on the exchanges and adjust the selling patterns to their customers. Aren't that what we are seeing?