Te be clear, I never meant that he should never eventually move to BTS. BTS is the complete Civ IV experience, there's no arguing about that.
Now, you are saying that it's better to install BTS because of espionage, Great Generals, more Civs Civs, corporations, random events, etc. But think about a newcomer. Think about someone who never played a civ game in his life. Think about all the things he has to learn at first: the roles of food / hammers / commerce, culture / gold / gpp / beakers, has to master the whole freaking combat system, religions, etc, etc.
Starting with vanilla is simpler.