I dont care what you call it, I would feel safer knowing everyone on my flight had a passport that has been checked rather than a blockbuster card or a fishing permit.
I'll call it pure revenue protection as well. As already pointed out BA and BMI do not normally require any form of ID for domestics. BE require ID but accept my company ID. EZY will accept driving licenses. FR are alone in insisting on a Passport of EU ID card for domestics.
EZY, BE and FR all insist the requirement for ID is on security grounds but that is complete and utter bollocks. What they are trying to avoid is people (companies in particular) buying up loads of cheap tickets months in advance on routes their staff fly frequently and then issuing the tickets to anyone to use. It also prevents the resale of tickets through auction sites such as ebay.