I don't think that's entirely true. The DMCA has a bunch of exceptions for things like "interoperability" and "research" that are somewhat vaguely defined, which someone who was subject to a DMCA suit could use as a defense. This rulemaking process carves out a subset of those where the Copyright Office has determined that the activity definitely falls under those exceptions. But unless I'm mistaken, I think it's possible to argue other uses as well--- but you'd have to argue in court why your use was primarily for interoperability purposes. The advantage of doing things that the Copyright Office already declared to fall under those exceptions is that you wouldn't have to argue that point at all, because the issue was already decided.