Some discussions say the variable was still needed in old versions of either the application that dealt with it or the web backend, its not clear. Some sort of software that depended on the variable. In later versions they finally made the variable optional, but most people seem to just add it out of good habit. It could also be used as a fallback, in case the function resolves to nothing or so, not sure. Someone else suggested the last version found in the variable could be documentation itself as a rough guideline to see from when this install script was.
I find like the documentation is missing this information and should clear it up. For newcomers this would help.