(there are discussions over implementation details: is a eula that is only shown after you install the software which is in shrinkwrapped box and that says that breaking the shrink wrap constitutes acceptance valid, for example. Those corner cases are beside the point, the thing is that the concept of a contract that regulates the use of software is broadly accepted, to the point that the actual simplest case isn't even litigated over since it's not a point of discussion.
There is no need to sign anything to make a contract. I don't know where that idea comes from, it's so misguided I don't even know where to begin. When you go to Starbucks and order a double frappuccino latte with extra whipped cream, and the girl behind the counter gives it to you, do you then say 'I'm not paying because we don't have a contract'? Of course not, there is a contract: they offer to sell coffee, you accept by ordering, the result is an obligation on their part to deliver coffee, and an obligation on your part to pay for it. No signature or paper or whatever needed.
To make my point clearer: You can own a physical device, but the software (IP) on that device is not your property. Is anyone familiar with court cases that might set a precedent if the root key is considered a software feature or a hardware feature? My bet is Sony is claiming it to be a software feature, and thus, not part of the property you purchase when you buy a PS3.
I buy a PS3. It is a computer loaded up with a OS to which I have a license. I can do what I want with the hardware, but the software isn't mine. An encryption key (in my mind) is a software component.
I paid for a product, I own it. If Sony wants ridiculously extended protections that turn the arrangement into some kind of conditional rental, they'd damned well better force the Walmarts of the world to have us sign documents to that effect at the point of purchase. This implicit agreement stuff is nonsense.