Can you cite sources for these claims? I've found it's very hard to find good scientific sources for the effects, but all of the research I've done on the topic suggests that you are grossly underestimating the effects.

Here is an example: http://www.amazon.com/Earth-Abolition-Stanford-Nuclear-Serie...

And here is another terrifying account of the effects of a nuclear explosion:

http://www.animatedsoftware.com/environm/no_nukes/tenw/nuke_...

And another good source which shows just how destructive a bomb would be on a major metropolitan area:

http://www.nuclearsecrecy.com/nukemap/