I think people simply have a habit of categorizing things to make them easier to understand and easier to remember. We associate many things with eras, generations, periods, dynasties, etc.

The web is always evolving; it's just easier to consider a particular time frame 'Web 1.0' and the next 'Web 2.0'. From my viewpoint, it seems as if each 'Web x.0' will/would occur after each recessionary cycle.

Then again, why try to make sense of something like this that is still so new?