I don't think there is any specific rule in this case. Like you said, they didn't reissue the ticket so it would seem that the ticket is still valid as is.

I'm wondering if AA is really going to let me use the U.S. segments of my owe that were cancelled because of the attacks, even though I have subsequently taken the segment from the U.S. to Europe. At least that is what they said at the ticket counter. But I am sceptical.

On the QF PER-AKL segment now becoming two, I would think you would have justification to get a free additional segment, as it was QF's change not yours. Having said that QF are being pig-headed right now as far as I am concerned, so I wouldn't expect them to be overly generous.