This isn't necessary, if you notice in the gameplay videos, there is plenty of ammunition laying around. If they input these "player ammo drops" they would need to re-balance the structure of the other ammo drops. They stated in an early video that you could get ammo from stores if you run out. Also, there is ammo caches around the various areas where you will be engaged. You can notice these in the videos of the story quests. TLDR, there is enough ammo.
