There are threads on both this forum and the Chase forum about people being shut down by the big banks. It does happen -- probably a lot more than people get shut down by airlines, given the credit risk and regulatory situation involved -- but typically banks shut people down for things much sketchier than buying gift cards to get the airline fee credit.

I'd imagine Amex is well aware that people were buying gift cards and their comment on the matter is the recent change to not have them reimbursed any more.

Amex has also taken some action against people who do various sketchy or pushing-the-limit things with sign-up bonuses, which is more akin to the AA situation, but there Amex's actions seem to be more focused on reducing the number of future sign-up bonuses such people can get, and occasionally clawing back already-issued sign-up bonuses.