Expired DL / permit = no longer valid ID?
So my brother was trying to fly from CVG to GSO last week with an expired learners permit (had expired in May). The TSA person inspecting IDs would not let him through, and then would not accept his student ID as a secondary form of ID (I can understand the latter, as his uni is not a govt agency). Anywho, he eventually made it through but only after missing his flight and having to take a later one. Here is what I don't understand... when one's ID (be it a DL, Learners permit, or whatever) expires, one certainly loses the privileges granted by that ID... BUT one's actual identity certainly does NOT expire. Why should it matter to the screeners whether the ID has expired or not? My brother still looks the same as his photo on the learner's permit.
As a side issue, I seem to remember, in the past, being told (by the NC DMV, no less!) to hold onto my expired DL because if I lose my current one, the old one could still be used "for identification purposes"!