Mainly each nation is based (roughly) on the culture/mythology of where it's placed on the old world map I think. With some exceptions...mainly the aquatics, ermor, and caelum. Also I'm not certain of where abysia comes from either. I think caelum was just because adding flying races is fun for the variety. Nothing quite like extreme mobility but weak fighting power.
Although dom 1 caelum mages were abusive enough to fight for their armies...
But drow as such would seem out of place in dominions...maybe somebody will make an d&d mod or something...machaka would make a good drow base for that because they already have the spider thing down.
