The term "spectrum" is a bit misleading and gives the impression of being one-dimensional, like an "autism score from 0-100". The very page you've linked to shows it's a bit more multi-dimensional than that. Essentially, there's a collection of different symptoms (say, ABCDE), and if you've got some of them, you have a Pervasive Development Disorder (PDD). If you've got ALL of them (ABCDE) you've got a really bad case of utterly low-functioning autism, but that's fantastically rare. If you've got ABC but no problem with D or E you might have Asperger's syndrome, if you've got ADE you might have "HFA", if you've got some other combination they'll just call it "PDD-NOS", which is a kinda catch-all for "other"... Never mind even more complicated things like "A and B and a bit of occasional D and E" which you might find in typical testing.
Back to the "autism score from 0-100", one sufferer's 50% might be precisely the opposite 50% to someone else's 50%, showing a totally different set of symptoms out of the "whole set", they'd be good at different things, bad at different things, and need to accommodated in fairly different ways
"It's complicated" :-(