The +2 piercing armor is just there to give the Macedonians some advantage and to balance the game better. For one thing, both Greek and Macedonian troops were practically invulnerable to archery attacks, obviously the game would be unbalanced if this was the case. Apparently the Macedonians had slightly heavier shields and less body armor, this is why they have their +2 advantage. As for their longer spears, these would make them move slower, who would want a unit any slower than a hoplite already is? It would die before it ever got 3 spaces from something else.
In reality the Persians should have the chariot and the scythe chariot, but they don't, this is because someone decided that Persia would be too strong with "the wheel". Everybody in this period (in Europe & Asia anyway) had the wheel, but for balance issues the Persians don't have it. I personally think that that makes them a crappy civ. It's a bunch of BS anyway, so who cares?
Themistocles
[This message has been edited by Themistocles (edited 11-06-98).]