In real life it wouldnt matter to me if the enemy was slinging bullets, cannons or toasters at me. I wouldnt want to take the risk.
In AH the life or death becomes more of a "lets see if I can get him this time" thing. The reason the guys with cannons are more willing in AH is because they have shooting with them worked out. And they do more damage so why not? In real life the cannon guys had less ammo, and probably thought between the rate of fire of the 50 cals, and their own limited supply, it would be a better idea not to ho.