I don't think people are actually getting at the crew or how much leg room you have, it`s more of an issue with an ageing fleet.
Its a reported fact that the older an aircraft, and an aircraft that has high cycles and hours with start to suffer from reliability.
Plus they will require more maintenance, fatigue takes it toll on both structures and wiring not just seats!
Newer aircraft will take the punishment of short haul flights much more efficiently, which in turn will result in lower maintenance and operating costs.