Obviously AA serves a lot more cities from DFW than from LAX, which is why it has been talked about forever as a QF destination; in fact QF announced that the 6x747-400ER purchase 4 years ago was specifically to operate SYD-AKL-DFW service (which the -400ER could do but the -400 could not). Similarly for ORD; QF not only announced SYD-LAX-ORD service but sold tickets (and was a week from the start of service, when it decided not to but to use AA codeshares instead). LAX has excellent service on AA, enough to be classed as an AA hub, and QF has been pretty happy with using LAX for its primary traffic (to the point that SFO's attempts to woo the A380 business away from LAX has been unsuccessful so far).

Leisure travel cares about price first, and Disneyland second. DFW-SYD will always cost quite a bit more to operate than DFW-LAX-SYD (my guess is 10% more, it is certainly in that price range), so the lowest fare will never be via DFW but out of LAX. Number of connections doesn't enter into it (or rather most people pick a routing with an extra connection for a 2% drop in fare, much to my amazement -- of course on FT everyone is picking the long way round for the miles).