Warrior Ancient and Medieval Rules

Maybe I'm missing something.

Could someone explain why the incendiary missile factors are the same
as artillery?

I don't believe they would be that effective, but I'll admit not
knowing much about being shot-at by flaming arrows.

Scaring horses and other critters, okay I'll buy that. Most animals
don't like fire.
Burning down houses, seige equipment, camp equipment, all very
plausible. That stuff easily burns; ask some boy scouts.

I could see that armour is no deffence from fire, but that isn't
really how flaming arrows work. It's not going to explode, or anything
(greek-fire arrows?). I'm assuming its a burning rag/straw fastented
to a normal arrow, not a molotov coctail. A shield would still
protect someone normally wouldn't it?

But why a factor of 4 vs Heavy infantry with shields? Thats the same
factor as charging horse-driven lances! The whirling blades of scythed
chariots! The impact of an avalanche of falling rocks! Etc....

Why? (No, really, if I'm overlooking something that everyone else
knows/has read please tell me, I'll feel much better and be much quiter).

If there is no good reason:

Why not let incediary missiles have their "normal" missile factors
with the added bonus of scaring mounted and burning stuff down?

Noel.