While the government doesn't outright say so, logically the comparison prior to the checkpoint of the name on a BP to the name on a photo ID is the only "enforcement" of the no-fly list. Without that one check the evil "Robert Johnson" (actual name on no-fly list) could just book a ticket under a non-evil name, check in online, and proceed to the gate.

While I personally feel the no-fly list is an abhorrently unconstitutional violation of due process that serves no purpose for increasing security (especially since it could be circumvented by any 20-year-old who knows how to get a fake ID), several government officials including Kip Hawley are on record as saying the no-fly list is an important security tool.