It's a very recent change, just since the DSM-5 came out last year. In this case it is mostly just a change in terminology, and certainly not binding.
http://www.autismspeaks.org/dsm-5/faq#changes
What I mean about not binding is that if identity includes Aspergers, a person is free to continue using the term without being incorrect. It's probably more just an attempt to phase it out and user a broader definition for the whole autism spectrum.
BTW, my last long response wasn't the promised long response. I haven't gotten to it yet.