Not entirely true, especially if you don't know what you're doing and create it on a compromised computer or website. You can also lose or damage or it gets accidentally destroyed. And this is why I prefer the following option. Create a wallet with a client that can be restored from a seed that you write down. Then write your private keys down safely. Then back-up your wallets safely on external mediums like usb drives or a cd-r. This way you're three times protected. Lose your wallet or it becomes corrupted? Then you've got the private keys written down. Lose the private keys? Then you can restore from seed. Don't ever just rely on one back-up or way of backing up because so many things can go wrong.