The reason to call it a spectrum is that the affected have often the same underlying mental and behavioral patterns, but spread across a wide range of severity from high functioning to uncommunicative.

I don't know how helpful it is to draw fine distinctions when the causes and effects of autism are still so poorly understood. For the non-expert, becoming aware that there are many people with related conditions of speech, social, and motor delays and disabilities is a much more important bridge to cross.

I basically buy DSM-V's decision to lump all the autism spectrum disorders under one label for now. It is an acknowledgment that up to now, calling someone Autism Spectrum Disorder or Asperger's Syndrome or Pervasive Development Disorder - Not Otherwise Specified was a highly subjective distinction without a difference. But it did make a difference in terms of the conditions health insurance would cover, to the detriment of the ASD person.