This makes perfect sense and I used to believe the same way 100%. To have weapons prepositioned and not to use them, risking discovery or degradation of the weapons, doesn't make sense. But then sometimes I think about the mindset and ideology of who we are up against and I realize that what makes sense to Islamists may not be the same as for you and me.
Let us imagine for a moment that it's true, that bin Laden has nukes in basements somewhere waiting to be used. The hard part, sneaking them in, is already done (according to the recent interviews, before 9/11). If we note how hard it is to find two men, Saddam and Osama, in a vast expanse of territory, it would be no easier for us to find these weapons. You can be sure they would be shielded and placed somewhere innocuous with no traffic. Why then haven't they been used?
If bin Laden (or whoever) wants to be the Mahdi, everything has to line up just right in his little magic show. He needs to be able to wave his wand at precisely the right moment, in order to agree as closely as possible with interpretations of the Islamic prophesies, and strike when some event of significance occurs. It might be on a certain date, or in response to an event, whatever will wow the Islamic man on the street. Al qaeda is, if nothing else, patient. They don't do anything rashly on impulse. They wait for the moment.
OTOH, all this blustering about WMD in the US could be total abject crap, just to scare us while they laugh. We really won't know unless something happens...or doesn't happen. As to the recent warnings for NY, LA, DC, there is really no sense in the gub'mint raising a big alarm and even worse, prompting an evacuation. Imagine the cost and chaos from such an evacuation. Idiots like Daleel and his buddies would like nothing better! And of course if we did evacuate, they would not strike. They would let the evacuation run its course, let us cry wolf, let us curse our stupidity and return to normal...then strike.
Which leads us back to the eternally good principle of not freaking out, there's absolutely nothing we can do about it if such weapons really are in place. Let's just live our lives, being watchful but not paralyzed with fear. And be thinking about what we would do, after...if it should come to pass.
They aren't in basements. My hunch is that they are in a apartment/condo building near the top floor of a crystal city building, likely encased in lead. They were snuck in using a refrigerator box from best buy.