They seemed to have started this back in Nov...
I had a flight booked since Aug, but about a month later, no more seats being sold.
Ended up getting re-routed on the VA bird for the same day (had option of moving days to stay with DL)
From what I've seen - as i fly LAX-SYD at least twice a year... is alot of empty seats...depending on the day. Plenty of coach haulers occupying a whole row to themselves (1 per three seats...asleep)
Makes me jealous as I sit up in the luxurious C+ seats with my wife and daughter.
So, in form with DL strategy to fill birds to 95+% capacity, taking a day off, letting a bird sit and filling up the seats on the rest of the week makes perfect economical sense.