In the SATN blog he maintains with David Reed, Bob Frankston writes about this:

If this story is indeed correct then it's either a fundamental misunderstanding of what email is or how it works and/or indifference to user needs. It will be far worse if ATTBI.COM gets repurposed and people get names that are on spam blocking lists and have other meanings. It's like treating phone numbers as paths through Strowger switches instead the table entries that they are. But at least with phone numbers I can understand why the carriers are willfully stalling number portability despite the proof of concept in 800 number portability and call forwarding. In the case of ATTBI it's not obvious what is to be gained by forcing such a change as opposed to simply shifting emphasis to the new alias.

At a higher level it is just one more example of why the idea of forcing the DNS to serve the incompatible purposes of being a source of stable handles and transient commercial identifiers is so flawed. My email handle shouldn't change if my carrier switches equipment or ownership or if I move or if I change my last name. Conversely if I have an (additional) address associated with my role, that address should work to reach the person handling that function and not any particular individual. There is no real technical problem with doing this. The real difficulty is in the lack of understanding that leads to changing people's email addresses (a form of their real names) just because of some reshuffling of share ownership of corporate entities.