Even web wallets which were designed solely to be a wallet are not entirely safe, this looks like investment, meaning when you deposit Bitcoins there they are free to work with it and earn money then pay you a fraction as interest, if they wanted to let you have access to private keys then why not pay interest on 16.3M bitcoins? because those coins are owned by people having access to their private keys.

They must've some big reserve to be able to act as a interest bearing wallet, but that could only be profitable for us if we were to deposit large amounts and not a few dollars worth of Bitcoin.