There's only two reasons that a story about a "terrorist cell" gets published - either a) it's been shut down and is no longer a viable threat, and thus is not important to any real security work, or b) you're trying to scare the public.
My money's on b), with BushCo looking for a way to bolster sagging Republican fortunes in the polls lately.
If this was any kind of "real" threat, you wouldn't hear about it because that would compromise an investigation - and possibly the lives of people involved in that investigation. (Remember, the really dangerous people aren't on the "no-fly" list - we don't want to "tip them off")
My money is that this is pure propaganda - based on the obvious (namely that underground cells are moving about the world on a daily or weekly basis to begin with). There's always somebody plotting something - that's why covert intelligence gathering is necessary. When it hits the headlines, it's either no longer important, fictional, or someone really screwed up. If they have leaks that big in the US intelligence gathering world, then the various organizations have a big job to do cleaning up their own houses. Otherwise, someone's spinning a yarn for political reasons.