Not wanting to defend QF but,

1. upgrade seats are taken from the standard J inventory so if there is a J seat for sale they will give it to you as an upgrade. Of course some J seats on some flights are reserved for late ticket sales and the like. Also that there may have been in your instance, no shows, late intl connexions or equipment changes allowing J seats to be available on the day. I doubt that it is the implication that QF is trying to restrict upgrades.

2. For use at the airport, I think QF and AN are trying to avoid the USA situation where planes are continually late often due to people upgrading with coupons and the like at the airport and the need to clear with DM lists. Far simpler to do it by phone, and have it all setup up at checkin. Nothing worse than being in the elite line and having the person infront take for ever due to wanting to use coupons etc etc etc.

But the 24 hour rule is ridiculous!

Mark