There was no mention of any surcharge for the A380 when I booked the trip. In fact, we had confirmed seats on the SIN-SYD leg on A380 when I first booked (and payed) for the tickets, but we had to change dates, hence the waitlisting.
The RTW ticket was priced at the standard *A rates for <29000 miles (even though the re-routing through HKG broke the mileage limit, we were not charged any extra bacause this was a non-voluntary re-routing)