Qantas told me the 380 is used on L.A. - Sydney runs but it does not have the capacity to go Sydney - Dallas. The 747 is required for that, and I have taken it many times.
"From 28 April 2016, Qantas will be operating daily round trip non-stop A380 services between Dallas/Fort Worth and Sydney, Australia, offering customers convenient connections on our codeshare partner American Airlines from over 50 cities in North America into DFW. +http://www.qantas.com/travel/airlines/dfw-texas-australia-deals/us/en
Maybe they forgot to tell the crew. My recollection is that it does have to stop in Brisbane on the way back because of fuel issues westbound.
There is a whole row of the double size 380 gates at LAX. That most A380s I have ever seen in one place.