Lots of good points from orbitmic.

IRROPs handling is a rather like insurance. You only really discover its flaws after disaster strikes.

Happily, although I seem to be plagued by delays, I haven't had a catastrophic IRROP for a very long time. I am, however, not confident that if, at 5.30pm some rainy afternoon in Pittsburg, my flight back to London were cancelled, I would have access to a reliable and effective means of getting rebooked. Given that my experience of dealing with the Indian call centre (to which GGL calls are diverted out of hours) is that they can barely be relied upon to revalidate a ticket after a minor schedule change, I have very little confidence that they could handle rebooking me from Pittsburg (whether on AA or another carrier).

Being good in a crisis is one of the key performance indicators for GGL so far as I am concerned.