When you hold your bitcoins inside Coinbase, they aren't part of "your" wallet. Coinbase works like a bank. When you deposit $100, they don't mark those bills as being yours. Instead they are commingled with everyone else and the bank gives you a promise that when you ask for your $100, you'll get your $100 back. Not that if you gave them a $100 bill, you'll get back that exact same bill. Coinbase works exactly the same way. This means that you can transfer Bitcoins between two Coinbase accounts (a) instantly, and (b) without incurring any transaction fees --- because such a transfer doesn't actually go through the blockchain.
BTW, Coinbase and other similar companies claim to be a full reserve bank, but unless there's an audit, there is no way to tell from external observation that they aren't playing a Mt. Gox game of being a fractional reserve bank without bothering to tell their customers.
So how does this relate to BCC/BCH? Since each Bitcoin customer doesn't have their BTC in a separate wallet, in order for Coinbase to support BCH, or any other random fork of Bitcoin that might take place in the future, they would have to track when your BTC was credited to your account, and then create a separate BCH account to track the BCH. Then if you ask to withdraw your BCH in USD, just as you are entitled to do with BTC held in a Coinbase account, Coinbase would have to find an exchange that supports BCH, and sell some number of BCH on your behalf.
Coinbase has elected not to do this, and gave all of their customers ample notice that if they wanted to participate in the BCH experiment, they would have to ask Coinbase to transfer their BTC into their own private wallet. (I'm not a lawyer, but I'm sure the fact that they did give notice is going to be something that will be mentioned as part of their defense if and when a lawsuit is actually filed.) When I withdrew all of my BTC from Coinbase last week, the transaction which Coinbase executed to transfer "my" BTC into my own wallet had "change" that went back to a Coinbase private key. That's another clear indication that "my" BTC were not held in a separate wallet, but rather commingled with other Coinbase customers' accounts.
BTW, Coinbase and other similar companies claim to be a full reserve bank, but unless there's an audit, there is no way to tell from external observation that they aren't playing a Mt. Gox game of being a fractional reserve bank without bothering to tell their customers.
So how does this relate to BCC/BCH? Since each Bitcoin customer doesn't have their BTC in a separate wallet, in order for Coinbase to support BCH, or any other random fork of Bitcoin that might take place in the future, they would have to track when your BTC was credited to your account, and then create a separate BCH account to track the BCH. Then if you ask to withdraw your BCH in USD, just as you are entitled to do with BTC held in a Coinbase account, Coinbase would have to find an exchange that supports BCH, and sell some number of BCH on your behalf.
Coinbase has elected not to do this, and gave all of their customers ample notice that if they wanted to participate in the BCH experiment, they would have to ask Coinbase to transfer their BTC into their own private wallet. (I'm not a lawyer, but I'm sure the fact that they did give notice is going to be something that will be mentioned as part of their defense if and when a lawsuit is actually filed.) When I withdrew all of my BTC from Coinbase last week, the transaction which Coinbase executed to transfer "my" BTC into my own wallet had "change" that went back to a Coinbase private key. That's another clear indication that "my" BTC were not held in a separate wallet, but rather commingled with other Coinbase customers' accounts.