It was a hypothetical.
If such a network exists in a state/city/region, it only exists because it escaped detection, and I doubt we are so bad and they are so good that this is possible across the board. But it could happen in key areas.
Think about it this way. Before 2001, we were trying to deal with UBL by having "subcontractors" (Northern Alliance folks) track him and possibly eliminate him (but we were never serious about that it seems). When it came time to get serious (post-9/11), we went in ourselves to lead the effort. (To get a job done right sometimes you have to do it yourself)
Turn the tables. Operations against the US were done by AQ, but they are "subcontractors" in the terrorist feeding chain. While other nations' "special forces" may not seem so "special" to us, they are much more threatening than UBL, Zawahiri, or Zarqawi. They (AQ) for the most part are not and never will be trained "professionals", but if "unprofessional" AQ has sleepers, that means the "professionals" (enemy intelligence and special forces) have a significant presence here as well.
They are not all working at the UN.
Wow. Sobering indeed.