Actually, no it is not. Here is a picture of Hiroshima before the war:
Here is one from after:
What you should pick up on is how there are structures still standing and how those structures differ from the ones that are not. I don't imagine it will take long for you to notice the problem with presuming LA or Seattle would look like Hiroshima.
The whole loose nukes paranoia is likely exaggerated if not deliberately fabricated. Hell, if there are any nukes unaccounted for out of Russia's stockpiles I would not be surprised if it turns out they were secreted away by the Americans, the Chinese, the French, the British, or even the Israelis. No way would these things be sitting on the black market for long and no one is going to pay nearly as much money as a major nuclear power looking to take a nuke off the market and get themselves a handy off-the-books weapon in the process. Just as likely that Russia itself used the chaos to take some of its nuclear stockpile off the books. Like dirty bombs, I suspect it is basically just another shrewd propaganda technique employed to get the public behind some policy initiative or just keep them terrified and ready for anything the establishment might throw at them. All about creating the siege mentality and distracting the people from things like the hundreds of thousands of random citizens who have lengthy dossiers about them at the NSA because they were in the wrong chat room or discussion forum.