It seems that someone applied the version control idea to the web, with the intention of remarking the differences between the read-only Web and the interactive Web we are dealing with today.
1.0 is the mark for the static content, dotcom dissaster and the raise of internet development.
2.0 is not just blogs, on-line video, wikis, and even more. 2.0 is the awaken of the open collective efforts and their results. Maybe hundreds of projects died in the way, but the important thing is that the new ones learned from the fallen.
3.0 maybe the Web in 3D, a semantic effort, or an omni functional platform. Who knows it? The point is that individuals and companies are investing lots of time innovating. So 3.0 may not have a unique characteristic, but many.
And what about when we reach the Web 10.0; or as Apple states, X?
