Ok, I've been away. So, lets clear a few things up:

1. Longbows were used around 5,000 years ago at least, just not as massed war-weapons because Celtic warfare always remained somewhat heroic in nature.

2. The pilum does not have lowere damage, but lower attack.

3. The pilum is a heavy weapon and therefore traveled more slowly through the air.

4. Ergo, if you are not wearing too much armour a thrown pilum is easier to dodge than a lighter javalin.

5. RTW has no "dodge" defence stat to calculate how likely a soldier is to dodge a ranged attack.

6. So, we nerfed pilum attack to reflect the fact that lightly armoured troops were more likely able to dodge this form of javalin, but gave them AP to reflect the fact that if they did hit they were more than likely to skewer you.