no inasero. Combined degrees and Double degrees are used interchangeably. In a combined/double degree you get 2 degrees in one course, not 1 degree. When they say a course is a combined degree, it means the two degrees are integrated and supposedly optimised in this sense, hence it is better than doing 2 separate degrees. This also means u can finish 2 three year degrees in the course of 4-5 years.
What you said about 2 separate courses to get 2 separate degrees is not coined a double degree. If you do most of your first degree, transfer to second and do most of that, then complete both degrees together, that is simply doing two degrees and a method used to be eligible for prolonged HECS and government subsidized fees. This will usually take longer as you will probably have to do more subjects and majors (many of which you will find redundant in an integrated field). Still, all courses have a degree of flexibility and if you are doing a combined and you really want extra majors you can work something out with the course co-ordinator and get it approved by the dean. Its logical to just do the combined/double if you can.