"Autism Spectrum" is a deliberately vague term that has been created and stretched to bring a variety of minor social and emotional functional differences under the general label of "autism". As far as I can tell, in the US the major purpose of this has been to divert special education funding from severely impaired children to less-impaired children from higher socioeconomic strata, and it has been very effective in doing so.
So to directly answer your questions, "Asperger's" (or whatever substitute term you find acceptable -- I'm perfectly fine with a substitute) is very useful to distinguish people with minor social and emotional functional differences -- those people who are, for example, able to hold down a tech job and post about autistic politics to Hacker News -- from highly impaired people such as my daughter who will never hold a job and whose verbal skills are at a three year old level.
These distinctions are vitally important to ensure that appropriate funding goes to these highly impaired children rather than being siphoned away to children of well-connected or politically savvy parents who are fully capable of succeeding in the mainstream educational system without aid.
There are plenty of people who the diagnosis of Asperger's who will never hold down a job. I'd hardly consider it "minor" even if it is relative to your daughter.
I am autistic, btw. An Autist. An Aspie. High-functioning. So's my brother. So's my father. None of us give a toss about these terms, but the subject of our traits and our getting on in society remains of interest.
