That was a response in Customer Support related to something similar in Gadgetzan.
However, there is a difference in Gadgetzan which is that the guards can go after the person being attacked, preventing them from responding with their own range attack (at risk of being killed by a guard and, I believe, taking a durability hit). In a faction city, that isn’t quite the situation. A Horde guard would not attack a Horde player. All actions to engage the person on the roof would be free of that risk.
I know I can walk up on the Bank roof easily, as well as drop onto roofs on the western side, but how does one “walk up on” the AH house roof or the Inn roof? Is there actually terrain that makes it easy to hop up?