Three problems:
1) Exchange operators, including operators and employees, might steal your bitcoins.
2) Exchange operators might lose the private keys to your bitcoins.
3) External attackers might compromise the security of the site and steal your bitcoins.
Since 2010, by far the largest problems are 1 and 3.
2 is something hypothetical that aren't even sure even happened.
Why is everybody talking about solutions to 2, especially solutions that do absolutely nothing to stop 1 and 3 (the ones we know happen all the time?)
On 2. weren't there some idiots who run a service on amazon cloud and didn't write their private keys to disk and when session went down all of the keys were lost...
I don't think it was exchange, but online wallet anyway...