It's actually not the same at all. What you are proposing sounds similar to what Dan said they're implementing. I want to see Bittrex, Poloniex, and any other exchange use one or more accounts (with different active keys) as cold storage, significantly reducing the risk of a large amount of liquid STEEM or SD from being stolen.
As it stands, if someone were to get the active or owner keys of either of these accounts they could instantly send the liquid assets to another Steem account. We know their active keys are "hot" because both are sending withdraws from the account.