At USYD generally for combined law degrees you only get one major in your other degree (rather than two). I know this is the case with arts, and I think its the same for commerce, but someone with a commerce background might be able to confirm that.
edit: here is a link to the 2013 undergraduate LLB guide for USYD http://sydney.edu.au/law/images/Feat...duateGuide.pdf
page 8 has a diagram of the course structure for a commerce/LLB combined student. It also appears that there is a compulsory private international law A subject for 5th year, so you get 7 electives (this is a relatively new addition).