Yep. CTP is for hospital bills and the like. Third party that you get from NRMA, Shannons, AAMI etc covers any other car in case of an accident (where you're at fault), but not yours. Comprehensive fixes your car too.
Driving without even 3rd party is one of the silliest things I've ever heard. It's REALLY not that expensive - and it's far more expensive if something happens and you get dragged through the courts.
As was said above, imagine you run up the arse of a brand new BMW - all of a sudden, you're getting quotes for $80,000, but if you'd paid $300-odd for 3rd party, sure, your company will NOT like you, but it's not 80k.