Could it not just simply be that Ryanair narrow down the list of acceptable ID's so that their staff can comfortably and confidently recognise and validate authentic ID's
As Ryanair use handling agents, who are looking after a range of airlines, I would have thought that having different ID requirements for different carriers would increase rather than reduce the confusion of the validating staff.
I am waiting for someone denied travel by Ryanair to challenge the requirement for photo driving licence or passport on a domestic Ryanair flight in the UK courts under the Unfair Contract Terms Act. In British law you cannot just write your own unreasonable terms and get away with it. The facts that BA and others do not require photo-id on domestic routes, nor do the CAA stipulate it, that photo driving licences have still only penetrated a minority of the UK population, and that passports for domestic travel are an unreasonable requirement, would I have thought lead to an easy win.