no one is responsible, that's the whole point. The thing runs by itself and game theory keeps it afloat - not a group of people. Else it's just like a company.
That said, the protocol isn't finished and you have people involved in maintaining and upgrading the protocol. Which is in no way forced down upon everyone: once they have an update everyone is free to choose to run it or not.
These people have influence (you could argue too much) about the future of the protocol.
> if your arbitrage trade takes away too much money from an account belong the core devs
This is not why these decisions were made at all, because some core dev instested in the DAO.
The decision-making and communities of Ethereum (this goes both for the clients, the blockchain, the foundation and the larger community) looks completely different today compared to 2015. There has been a lot of lessons learnt, debate and churn since.
If they same thing happened today, it'd play out completely differently.
See the Parity Multisig hack, for one.
Finally, it's a stretch to call the dao hack "arbitrage trade".
It is absolutely not. It is exactly the same from the value judgments of the ETH project, specifically "Code is Law". The DAO specifically went as far as endorsing that the software execution takes precedence over the reading of the English functionality spec.
The ETH system, but the core values of ETH, should do exactly what your arb contract specifies, and exactly what the DAO contracts specify, even and especially if that's not what the writer originally intended. To selectively reneg on that principle would be wrong for the same reason as doing it on an arb contract.
