Exchanges Hold A Lot of Power
The halting of new account creations by exchanges (Bittrex and Binance) shows the control they have and the power they hold in the crypto world. In the latest news, Bittrex has suspended the creation of Ethereum deposit addresses. I don't think this is necessarily being done for purposes of control, but is rather due to the inability to scale. The support network in terms of adapting to increased demand is considerably lacking. With so much growth potential and increased interest one would think this is something the exchanges would have thought of and made the necessary changes to adapt long before now so it did not have to come to temporarily closing very basic actions these exchanges perform. 
They sure do and literally billions of dollars have been lost to exchange either from them being hacked, losing keys or flat out trying to take advantage and siphon off the top.
I don't believe in exchanges I believe in holding it in your own wallet that you own then if anything should happen its your fault and not anyone elses but there is more risk being on an exchange you don't own the wallets.