If they truly have cold storage of their btc - yes, this system does improve security, as their cold-storage bitcoins aren't subject to electronic hacking, just physical intrusion. And, the use of encryption and HSMs can mitigate against even a physical intrusion as well.
Sometime in the next couple years, someone is going to come up with a relatively fool proof vault storage for bitcoins, we just haven't see it yet. (And Coinbase isn't sharing enough details yet for us to know whether they've put one together)
Sometime in the next couple years, someone is going to come up with a relatively fool proof vault storage for bitcoins, we just haven't see it yet. (And Coinbase isn't sharing enough details yet for us to know whether they've put one together)