On BTC, you could send things to the wrong address, yes. But you can't send the wrong type of currency or send it to a nonexistent address. In this case it seems like the contract has created the black hole (not the Ethereum blockchain itself), but that's even more absurd since someone ultimately should have control over everything that was put into the contract, regardless of the source.
Sending currency to non-existant addresses is how people encode arbitary data on the bitcoin blockchain, so definitely possible.
Giving a person control over the funds allocated to their smart contract probably opens holes where they can steal the smart contract's money, though obviously creating software that handles money and can't be updated is its own kettle of fish.
