I think the author thught about implementing culture like it is implemented in Starcraft (if we can say that between the Zerg and the Terrans, the difference is cultural) : different ways to manage ppl, different buildings, different units, different tech trees etc.
Someone reacted to the argument saying it would be impossible to make it in an historical outlook, because it would lead to a fantasy of what-things-could-have-been like (we don't know what would be the current Aztec tech tree if they had repelled the Spanish for example).
As for I, I'm against because all the games who have clearly separated tech trees for each faction have short ones. We have barely 80 techs in Civ3 (and it is unprobable any Civ game will have more than 100), that would currently be 5 advances per tribe, 16 advances per group.
But the author says other things definately worth reading :
http://www.joystick101.org/?op=displ.../12/222013/422