9/11 belies the notion that Osama is into high maintenance, high cost operations.
They're not going to bother with weapons they have to maintain, from twenty and thirty years ago. They will procure a working nuclear weapon one day, and set it off the next. They can't afford to be lugging around a nuclear bomb like it "Weekend at Bernie's" until they're ready to use it - whenever that is.
As do the London bombings
Not to mention that the nuclear triggers have very short life spans.