Originally Posted by JohnAx
Some airlines/routes offer no or very limited A availability (e.g. some hot AA domestic routes)
Good point -- but remember that you can ask for a seat to be released for you, and the AA RTW desk is remarkably successful in getting seats released on some of these routes. The problem with A on AA is that A is also used for upgrade inventory which distorts availability on the hot routes (but AA does distinguish between revenue A and upgrade A, somehow).