fair enough, i see your 'strawman' and raise you one 'argument' (well, hopefully):
-if- you think there is any reason whatsoever to balance the game towards making the "less obvious" weapon skills at least marginally useful for more than just a quick fraction of the early game, then, barring AP-based and/or melee sillyness etc.., you'll probably end up with ammo scarcity as one of your mechanisms of choice.
and since RPGs are great at keeping resources like ammo consistently scarce.. *sigh*
at least AP-differentiation can easily be maintained throughout the game.
i suppose damage types/status effects are a 3rd possibility?
i personally don't play turn-/AP-based games for the sheer speed thrills; if there is nothing for me to even consider [hmm, more damage at longer range or less damage at shorter range.. decisions decisions..] during a turn then combat becomes quite excrutiatingly dull and repetative quite double-quick (as in: wow this is taking forever..).
@Snakeoil: they're hardly going to base AP amounts on stats that are not in the game. so, yeah, it may indeed be based on some of the CLASSIC stats/attributes. i'm having trouble deciding which stat (in your example) i think should determine what.. especially speed vs. coordination. if i switch them around they kinda make just as much sense to me..
Edit: @Ronin73: idk, i've always felt that 100-AP systems are all grain and no.. advantage.