i agree al. has a finite fatigue life, and in theory in can break catastophically. Empriically, my al. frame has been ridden daily for over 16 years. On road and off. Gathousands of miles annually. No failures and I have full confidence in the frame. Likewise, must of us dont sweat the 'finite fatigue life' of our handlebars, which take a beating.
now, if i had throughbolted the downtube and the seattube, I may not have such confidence.