[rawatson]

I always thought x.y.z version strings (like Firefox 3.6.3, or similar) contained a bit of extra information about how development occurs which is often ignored.

When z is increased, that is the developers way of saying that "this is the least dramatic update we will make available to end users". Alternatively, an increment of a is a sign that "this is the most dramatic alteration in functionality we will make".

I think that part of the trend toward higher version numbers isn't just about having nice big numbers, but rather a reflection of changes in development methodology. Whether you attribute it to DVCSs or simple changes in developer culture, it seems clear that the "biggest possible" update has significantly shrunk in size lately.