Upon reflection, I think Seinfeld's actual words were very cautious and very carefully-well chosen.
He didn't say "I have autism". He didn't even say "I have Aspergers."
No, he said "On the spectrum." I think he used the word "spectrum" very deliberately.
"Spectrum" simply means that something falls between two points. In the literal sense of the word, everyone in the world is on the spectrum, with extreme NT-ness on the one end, and extreme autism-ness on the other end.
Of course, currently when someone says "on the spectrum" they mean that their own little dot falls close to the autism end than to the NT end. But nonetheless, I think Seinfeld's use of the word spectrum conveyed the message of not. He even said "On a very drawn-out scale..."
I think if people had listened more closely to his actual words, there would not have been this fuss.