Sorry for never getting around to answering your question - I've just seen it after revisiting this site for the first time in a long time.

Yes. I turns out that on the AA 777s we fly (the Atlantic ones between London and Chicago, LA, etc), all the non-bulkhead seat aisle armrests are movable. The release button is on the inner side of the armrest, hidden by the backrest cushion.

What surprises me is the number of AA flight attendants who don't know this. On several occasions, I've actually had to show them how to do it because they saw me doing it and wanted to know how.

Similarly the armrests on the old 757s they use to Hawaii are all movable - in this case the release is a sliding metal latch on the underside of the armrest.

Alan