From my experience with Total War games CA always divides the factions into certain groups that have a similar base (animations, units, graphics etc) it makes it easier to develop the game. In M2TW the factions were divided by religion, so we have muslims, catholics and orthodox nations, the last actually include some catholic one. They have their unique aspects, but are still largely similar. Due to this fact each nation has a lot of inaccuracies and while they are certainly important, like it was pointed out in the original post, they are still too numerous to correct when one looks at all the factions.

PS. The sentance below was very amusing

Quote Originally Posted by dopp
Feudal armies could be very large, but only a tiny fraction of them would actually be hardened soldiers (knights, men-at-arms, mercenaries like longbowmen). The rest just scream and run around a lot when the fighting men are defeated.