I believe we did the right thing in dropping the bombs, but there was no way we would have had a million casualties. If you look at last ditch Japanese rifles the Japanese were just about done with making weapons to fight with.
I seem to remember seeing a video where the citizens of Japan were training to be the "last line of defense" in an invasion. They were training with what appeared to be pikes. Now, the question would have to be whether those citizens would have thrown down their "weapons" or not, but my guess is that there would have been soldiers behind those civilians with weapons to kill said civilians if they didn't fight.
So, yeah, the million casualties very well could have been a valid number.