I was wondering the same a few weeks back and called QF to check, if you do not board the first flight it will cancel subsequent legs. You can ring to get it changed and reissued but that may incur fees.
That's because LCC's fly point to point. You miss a connection with an LCC you're screwed. Traditional airlines on the other hand guarantee that you'll get to your destination, so if you miss a connection they will automatically re-book you onto another flight.
Given traditional airlines treat A-B-C as simply A-C, it's quite reasonable that if you don't check in at A, then they have no obligation for B-C.
LCC's on the other hand you fly A-B and then B-C.
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