AJAX indeed does power Google's AutoSave.
The whole back-button conundrum-- was it any better with old-school cgi apps? Those are horrible in comparison.
web 1.0 also is a catchphrase, but it is a derogatory one coined with web 2.0 that means, this site is old and needs some work.
To a certain extent it doesn't matter... take a look at http://www.web20generator.com/.
It's more of an umbrella phrase that people use to describe things.
For all that it matters, we could be at web five-million point three.