I have been trying for some time to divine the true meaning of the phrase "Web 2.0".

I finally get it.

It's all just a big misunderstanding over pronunciation. Sure, it looks like you're supposed to say "Web Two-Dot-Oh" when it's written down. But it's actually just a chat-speak way of writing the phrase "Web too", as in:

"Web applications can finally do some things that Java applications have been able to do all along too"

• Local validation? Check.
• Client-server interaction? Check.
• Improvements over traditional HTML GUIs? Check.
• More interactive browser applications? Check.

Of course there are plenty of things they haven't gotten to yet, like offline usage, runtime performance, development tools, ...

Maybe they're saving that stuff for "Web Free"