Hmmmm I can't speak fully on this topic (but I will have a go) @cybernatic I'd appreciate other people's input into this.
I can only really say from the way I think I understand it.
There would likely be some sort of smart contract on the Ethereum network that Slock.it created. This would be like the entry point to all applications using the USN. An entry point DAPP that connects to the USN.
Everything Slock.it do is going to be open source right. So the code will be clearly visible, and other companies will be able to see this and interface with it. They are giving away the tech so it is mass adopted to become a universal sharing network. But because the smart contract is either only ever ON or OFF (1 or 0) it is only ON if the myriad other devices and their contracts satisfy the correct conditions to interface with Slock.it's DAPP.
Comes down to the whole beauty of the blockchain, somewhere there is a key that matches the smart contract on the chain, and you have to absolutely satisfy the requirements to use that particular DAPP to get it to say On or Off.
The way I read it, the DAPP once deployed by Slock.it, is the DAO's DAPP (anyone please correct me if I'm wrong) because we contracted Slock.it to build it for us. If they wan't to change the DAPP, they have to send us a proposal to change it, and we have to accept that or reject it by voting. They are bound to us remember. Like the One Ring to rule them all. They are the Nazghul and we are the all seeing eye of Sauron.
They can never change it without our permission. That interface into the USN with the EC will stay there for any and all companies, manufacturers and individuals to use, so long as any revenue they collect includes the DAO%
If Slock.it disappeared, we would just put to tender, or hire another contractor to take up the job, because its all open source.
The DAO holds all the keys, all ability to interface with the USN which Slock.it is making for us. They want to sell smart locks right, physical products. Bike locks, car locks, door locks, lockers etc etc. Its John Smith who wants to unlock Jane Doe's holiday home using one of Slock.it's door locks who pays Jane Doe to do this, and we take the DAO% from this transaction. Slock, after completing the contract, just makes and sells smart locks. This is the deal they strike with the DAO to get x million in funding from us.
You could hack the lock. But probably only using a hack-saw. Of course you could physically hack anything I guess by re-wiring and soldering the PCB, but then you can do that for anything. That's all accepted as part of the terms of the contract. But you couldn't hack the working smartlock by hacking the blockchain. No chance.