Department of Alarming Sentences

From the NYT:

Airlines are not required to report cash purchases, a Homeland Security official said.

We are talking of course about the guy who almost made it to Dubai after trying to explode an SUV in Times Square. He paid for the car in cash and for the ticket in cash.

Does this sentence above make any sense?  Shouldn't cash purchases of airline tickets be more prone to suspicion? Not everybody who pays cash is a criminal, but why not report those purchases too? Because we are still idiots when it comes to security at airports.