It is just that I have never experienced anything in between the 'normal' time it takes, and those instant immolation cases. And it applies to both rams and towers.
So if you guys have experienced equipment going up in flames after the first volley of archer fire or second, then it sounds more acceptable. But I have never been able to flame a tower or ram within three volleys at the least (only experienced instant immolation when I was the attacker).