I am not sure why you say Religion is not available in CivRev. It is an available tech being the one which unlocks the Cathedral city improvement and Fundamentalism government. The nation for your avatar, Ghandi of the Indians, gets religion as a free tech for moving into the medieval era. The Arab nation gets it as their starting bonus.
Do you mean that their should be specific religions associated with different cultures/eras? That is what your statement about communism seems to imply. I think Firaxis gets enough flak for having put the Arabs into Fundamentalism to start the game (awesome advantage though that is!). Their legal department probably is not large enough to handle the deluge of lawsuits which would result from more specific handling of religion in the game.