People also assume, in the car case, that the law will be rational about allowing them to circumvent restrictions. Locks on the hood? You bought the car, so cut 'em. It can void the warranty, but it can't be made illegal.

In fact, the law usually goes in the other direction: it's illegal for manufacturers to actively put in some kinds of restrictions, like first-party-only replacement parts or only-serviceable-by-manufacturer vehicles. Putting a lock on the hood, if it's intended to prevent third-party servicing, is probably illegal in the first place.