Don't get me wrong, I LOVE tall empires, nothing is more fun for me than running a tall empire. You concentrate production within a few cities, which leads to an exclusive right to build wonder. Your borders are small, but very far from cities -- much easier to defend. You can exceed almost everything, you just can't afford conquering cities without razing them. But what is my point: the main advantage of tall empire is population, which often exceed 40 in each city in the late game. It means that two atomic bombs or nuclear missiles can reduce this amount by 3\4! I remind, the whole production machine and tech dominance is based on size of city population and it can go nowhere within first turn of a war! Did someone really get a proof of reliable protection agains nuclear weapon?