It's called lying, and an airline should refrain from doing so. They can choose to put "recommended time at gate" if they want to post preposterous times (55 minutes prior? Really??).
AA does not post "gate closing", but "boarding time", on their boarding passes. This is the time when boarding is scheduled to commence; it is a standard 30 minutes for narrow-bodies and 40 minutes for wide bodies, as per union contract. It's a straightforward piece of reliable information, even though, as we know, all sort of things happen and schedules are not always followed or at times all employees concerned can agree to board before the contractual time.

I think that AA's posting a boarding time, instead of a "gate close" time, is better as is a safer piece of information for the less-experienced traveler. It most likely results in less people being late at the gate--which is probably why BA stations mangers [sic.] are fudging the numbers and lying on the BPs.