I think you are conflating the jailbreaking/rooting exemption and the carrier unlocking exemption. The exemption for jailbreaking phones will apply for the next three years (until it comes up for renewal again), while the exemption for unofficially carrier unlocking phones will only apply to phones purchased before January 2013.
Looking at the official statement about the unlocking exemption (pages 16-20 of https://s3.amazonaws.com/public-inspection.federalregister.g...), it sounds like the software on the phone controlling its access to the carrier is a copyrighted work. So if you want to circumvent protections against modifying it, you have to wrangle with the DMCA.
Silly me. And I thought that "effective technical measure" was against copying, not modification.
I'm no copyright scholar, but this seems like they lack jurisdiction about this, and/or are trying a power grab.
E.g., Bunnie Huang's NeTV device modifies an HDCP encoded signal in-flight, adding an image overlay. If what you state about unlocking is true, then the NeTV is also illegal, and the DMCA is even worse than everyone thinks.
I believe the problem with unlocking is that both copying and modifying require circumventing technological protection measures, and that modifying a program has legal ramifications similar to copying it - they're both fair use if you own the copy of the software and not fair use if you're just licensing it. Since the purpose of exemptions is to allow fair use, but it's unclear whether we own or license the baseband software on phones we own, the Copyright Office decided to approve but limit this exemption.
I'll show my work, since I'm not a copyright scholar either, just trying to interpret the official statement:
According to the summary on page 1, the questions are: (1) Are you circumventing a protection measure? (2) Is the measure protecting a copyrighted work? (3) Is your use of the copyrighted work non-infringing? [And according to pages 4-5, there's another question, although not directly relevant to your comment: (4) Is circumvention the only practical way to achieve the result of this use?]
The discussion of the unlocking exemption ("permits the circumvention of computer programs on mobile phones to enable such mobile phones to connect to alternative networks") starts on page 16. Page 17 includes an interesting bit about copyright:
"Proponents advanced several theories as to why “unlocking” is a noninfringing use, including that it does not implicate any copyright interests or, if it does, the conduct is permitted under Section 117 of the Copyright Act. In particular, proponents asserted that the owners of mobile phones are also the owners of the copies of the computer programs on those phones and that, as owners, they are entitled to exercise their rights under Section 117, which gives the owner of a copy of a computer program the privilege to make or authorize the making of another copy or adaptation of that computer program under certain circumstances, such as to permit the program to be used on a particular machine."
But then page 19 presents a concern: according to some legal precedents, the owner of the phone may not be the owner of the software, so he or she wouldn't have the right to modify it. It says "the Register was forced to conclude that the state of the law – and its applicability to mobile phone software – remains indeterminate." After some more discussion of licensing and ownership, it goes on to say "The Register therefore determined that some subset of wireless customers – i.e., anyone considered to own the software on their phones under applicable precedent – would be entitled to exercise the Section 117 privilege."
I believe all of this shows that the Copyright Office considered whether it had jurisdiction and decided that it did. I don't know enough about Huang's NeTV work to be able to guess about how the DMCA applies to it.
