I agree. I much preferred the way borderlands did it. You carried ammo for each weapon class (assault rifle, smg, pistol, shotgun, etc.). If you flat out ran out of ammo, you just switched to one you had ammo for. And for those saying "durr how do sniper bullets work for fusion rifle?!", well I dunno, but they apparently do since any green ammo box gives you ammo for any special weapon.