In theory you are correct, but you are neglecting the fact that speed limits are being lowered all over the place and for BS reasons.
Example - no-one speeds through a 60kph limited housing estate which has cameras.... hmm no revenue and no accidents so what happens? Yep, 50kph limit is instituted. People adjust quickly so no more revenue (and still no accidents)... next thing you know the WHOLE ESTATE is a 40kph zone!
Unfortunately this can and does happen anywhere in Vic.
There is a road near my parents house that was a straight dirt road with a 100kph limit, had a bit of traffic, was always graded and had 1 accident (single car) in 20 years.
Once day, VicRoads decide that this road should be sealed... with a 80kph limit. Okay, whatever.
Then they start putting mobile speed cameras on this road, then the limit is dropped to 70.... then to 60... why? There is no more development on this road than there was when it was an 80 zone. Accidents? Nope.
Whoa! Blind man shooting at the world!
You may want to look up how much speed cameras raked in for the Vic Government last year... $430m+.... AND the road toll is higher than the year before, so how can someone say that speed cameras are a successful safety device?
Making it tougher to obtain and regular mandatory re-testing (say every 5 years) via advanced driving courses to keep a licence would be much more effective in lowering the road toll and making the roads safer.