Eureka! The answer to the A380 economics question just came to me, in the shower. [Don't try to visualize that, it's not pretty]
It's not premium pax that save the day for the A380 on the Dallas route. The A380 covers it's higher costs by carrying an extra 100 or so 'tourist class' pax TO Dallas. It just can't bring them back.
So girls, be nice to those folks down the back on the way to DFW. They're paying somebody's bonus.
I even nutted out a little country song. It was a long shower:
'One Way Ticket To Dallas' - by Captain Gidday.
"We can take you any day to Dallas,
But you'll have to come back
Through LAX"