The popultaion cap is probably universal, but the pop. cost of the different races varies. Seeing that the elves have some of the strongest units, their units cost a lot more pop. then the orcs, who's units strength compared with the elves it a lot less.
"The flower of friendship blooms even in hell. On the sand where waves come and go, it leaves its petal as a memento. We will make it bloom again someday, The Okama Way!" - Mister 2, Bon Clay