I'm not so sure. For starters, the same reasoning can be applied to any number of nukes. "Hey, they have leveled each and every single one of our major cities, I think they did have as many as they said!"
And, after the first one was dropped, it's not like they asked if they wished to reconsider unconditional surrender. I mean, thousands of lives wasted just to make a point that didn't need to be made in the first place.
Anyway, this is a pretty good thread, let's not hijack it.