There also appear to be two different fonts used by the flip-dots, too...
That would likely be a result of years of experimenting with the best balance between trying to find the easiest display to read, while conveying the most relevent information. For example, the word "Central" taking up the entire destination board is exceptionally easy to read, but hard to understand - does the train go via East Hills, Bankstown, Regents Park or Granville? Likewise, "Central & City Circle via Liverpool, Fairfield and Granville" conveys a lot of relevent information, but it requires the text to be smooshed down, that it's often no help to anyone.
I believe the optimum solution to have been discovered in the form of the final destination being in enormous letters, with the via information being in smaller script underneath. The trick is then to find that unique via point that no other route uses. To state 'Campbelltown via Liverpool' is pretty useless, seeing as there are three ways to do so. However, by stating 'Campbelltown via Granville', we eliminate all other possibilities, because there is only one way to Campbelltown that involves going via Granville.
...which screams out the final destination but also supplies the critical via point, making a useful destination indicator.
Of course, if it was a bus, one could flip through...CAMPBELLTOWNVIA GRANVILLECAMPBELLTOWNVIA FAIRFIELDCAMPBELLTOWNVIA LIVERPOOL
...in a loop.