I think people are forgetting the major thing about nukes is they need guidance, without guidance what are they going to hit, which is why you need somebody like Iron man (who could hack in the GPS) or storm who could just take them out.
Also, you must consider that if they are invading the real world, would America really launch nukes against its own city's, for instance.
"Im Tony stark, and Im based in NEW YORK...."
Would we really be willing to sacrifice millions of people so easily? Im not saying we wouldn't, eventually, it would come down to that, we would and probably will have to sacrifice millions. But as I've stated it wont be as easy as see threat/push a button. We would first have to see if the person is just a loony or a real threat, and by the time we establish them as a real threat to take over the country/world, it could already be to late to even mount a counter-offensive.
Nuclear weapons are powerful indeed, but there are many steps we must take in the real world before we even consider the idea of a launch. And on top of all that, we would need GPS, and if Stark/Storm can take out a some major GPS. Do you think we could muster up the funds, let alone the shuttles required to launch satellites back into space? I think not.
Without satellites, the entire world would be blind. Iron man could be pounding Britain with Nuclear assaults with its own missiles, and we or no other country would never know about it. Storm could unleash a fury of blizzards on America, and again, No one else in the world would know what is going on.
Communication is key to taking over the world, anybody that has the ability to take away communication, has a shot at doing it.