If I remember correctly, Asperger's Syndrome was basically a significantly less severe form of Autism. Further those with Asperger's for the most part could function in society, not perfectly, but well enough for it to not be classified as a disorder. I admit, I may be wrong about this.
It makes sense to move it under the spectrum of Autism as it is basically the same underlying condition. It still came as a bit of a surprise to me, but then I was not really paying attention to the changes in DSM-V regarding autism, being focused on conditions more related to my own problems.