I'd have thought that there were far more factors outside of an airlines control, meaning contingency was more of a necessity.
Iarnrod Eireann control/own almost all aspects of their service - the stations, the trains, the tracks, signalling, points, all other trains etc so have far fewer outside factors that could adversely influence their service. Some still exist e.g. bridge hits, rock slides, leaves on the tracks...but not sure what the frequency of these events would be.
The thing that really annoys me on the DART service is where a train is left waiting for a driver changeover at the train depot just before/after Clontarf Road.
Or when they blame delays on the late arrival of another train, as if they have no responsibility for the 'other train'.