that is actually true. I haven't had the chance to play Arma2 until now, so I thought it might use the above mentioned position. Kneeling down is a way to improve accuaracy, but it it is very static.
If you spot a target on your flank you have to move your legs before you can actually take a proper shot at your target.. Many games portrait the soldier like if he was able to slide sideways with his knee in this case. I don't know how ArmA2 handles this stance, but in real combat you don't use this stance if you want to remain mobile.