It does suck that we all pay that much but all factors are involved with regards to insurance (at least from what I've been told and researched); location, car, statistics of accidents of that car involved in car accidents, whether your car is garaged or not (secured also or not), alarms, immobilisers, driver history, claim history, etc. I can only guess that there is a massive algorithm that all insurance companies have to fork us all over at any given time.
What kind of differences are we talking?
If you have a crash, your car gets fixed.
If it's a write off, you get cash.
That's really all that matters with compo insurance?
NRMA cover me and any driver of my car for example. I don't know another insurance company that matches that, at least not yet. There may be a few other things but that would require me to look at my policy in detail which I cannot be assed doing at the moment.