Bob, in TAAATS VFR plans often aren't routinely displayed by the system because there's every chance you won't require a service. I work en-route and if you call up requesting a clearance into TMA airspace I can look up your plan and activate it if I find one.
If I don't find one it could be because it's timed out as you left late and enjoyed a long lunch or you're early. These can be retrieved, but there's no point in looking if you never filed in the first place, hence the question.
Back in the good ol' days if there was no plan all I had to do was grab a paper strip, write a callsign, level and basic tracking details and we were good to go. These days I have to open the flight plan window, type in your callsign, aircraft type (correct ICAO code), departure point, destination, tracking points (all correct codes), level, IFR or VFR and aircraft rego (even if it's the same as your callsign). Then I have to activate the flight plan by putting in a reasonable departure time so that the flight plan track is near enough to where you currently are so the system automatically couples the plan to your transponder code.
None of which is terribly difficult but it takes time and when you're busy it might take several minutes and when you're separating aircraft this can be a distraction. We don't have assistants like they do in many other countries.
It's nothing to do with doing things a uniquely Australian way and all to do with the tools we're using. Help us feed the elephant on your behalf.