Correct me if I am wrong, but the fact that we can use all types of weapons and armors, wouldn't that be a good reason to give us a choice at rewards?
It would seem that if we were forced to wear certain armors, like a tank had to wear heavy armor, then I can see why there would be no choice at reward, because you would give him heavy armor.
If I am a light armor person, why would you giving me heavy armor be a good thing?