I agree with increased knowledge equals Increased diagnosis. From the 1980s to now is exactly when ASDs have been properly identified: my dh was a kid in the 80s, saw paeds etc but no one knew about aspies then. Nowadays it is well known in The medical fraternity plus the community, and there is actual funding to get help - of course rates have increased drastically.
In our case I am 100% confident vaccines were not involved - we can trace the aspie in dhs family back to well before vaccines were around! I can't speak for other families but think it is an unlikely theory. I am waiting to hear some of the research results from studies of pre vaccine infants and signs that might be showing then.
I just told dh about the pp about the Internet and he thought it was spot on - in many ways the digital world is perfect for asd people, so we might see an even greater increase due to more having families. Which in many ways is a good thing , cause as stressful as it is right now I know my little aspies will make the world a better place