From a comment I made before this ruling but which is now decisively confirmed:

The thing is, "not your keys, not your coins" is not just true technically, but true legally. If Coinbase were to become insolvent and decide to use your coins to repay their creditors, you might say, "Hey, you can't do that, that's my money!", and they would-- correctly-- respond, "No, it isn't. Read that user agreement again." They really are not your coins.