Their browser addon eliminates that risk, no?
yes, but not everyone uses it.
There is still the risk on blockchain.info that you have a keylogger on your computer and your backup file gets stolen. The ultimate solution will be a bitcoin account which is insured by your bank, like normal bank accounts.
I highly suggest using two factor authentication. This greatly diminishes the chances of your account being hacked and is available from Blockchain.info (amongst other sites). As many have suggested, I use the Blockchain wallet for day to day transactions and a paper wallet for "savings." I have no patience to download the blockchain and keep it constantly synced.