The point is more about even countries with a minimal nuclear arsenal being in relatively equal military footing as the countries with large arsenals because no country seems willing to risk losing one of their major cities to nuclear attack. So, threatening 100 cities is about the same as threatening 1 - no one will attack you.
That's pretty much the main reason north Korea hasn't been attacked since the Korean War: even without nuclear weapons, nobody wants to risk war when Seoul is all but guaranteed to be leveled.
