With blockchain.info you have the private keys, mtgox was the one with the private keys.
Blockchain.info you own the coins, with mtgox it was mtgox who owned the coins, cryptographically speaking...
Yes, its a better system for users because of this. Of course you are still needing to trust the functionality of the website and that it has close to 100% uptime.
Correct, assuming Blockchain.info claims are true.
If you have your keys you don't need 100% uptime, has you'll be able to move your coins if blockchain.info isn't available.