Well lots of people don't do priority boarding and aren't arsed about the overhead lockers.
On two of the last three flights back to the UK, I've seen Ryanair attendants randomly pick on a passenger about their bag size despite half the queue having similar or bigger sized bags.
The first guy got into an argument and got offloaded I believe (not a smart move on the last flight out of France for two days due to a strike).
The second woman managed to get her bag into the box but the way she was treated was appalling.
The attendant nearly went for DH cos he was carrying two bags - his own and our nine year olds. She was really rude (DH was unwaveringly polite).
But I think they have an issue either with overbooking or trying to squeeze a few more quid out of passengers and there's a directive out to get so many passengers per flight on rule infringements.
I think this one is just a way of ramping up the basic cost of flights for the cheapest tickets without being honest about it and so they can advertise the lower price.
One reason DH and I always travel light is to reduce time taken at check in and security. Having to queue for a pass will defeat that for many who use ryanair as a bus service.
I think there needs to be a balance between false advertising and fleecing those who are happy to go the whole no-frills.