Why versions??
The goal in application development is always the same: create the best possible software in the least amount of time. Yet the bar is continually raised, as demands from customers increase. To meet these demands, the platforms developers build on and the tools they use must get better and better—they must evolve.    -David Chappel, Chappel & Associates.

        I reckon, this software upgradation or enhancement or evolvement, whatever it is, can be called as versioning. The best example we can consider is .NET framework itself. Since its birth in 2002, .NET framework evolved version by version as follows: