While it is good to consider longer life for individual components, we must not forget the overall expected lifetime for the unit (the power supply in the present case). There may be other components that may have considerably lower expected life within the same power supply. In turn, the power supply may be used in some units that may be have a quite short life cycle.
The designer of the power supply may not have much control on the life of the final product in which the power supply may be used. Therefore it may be prudent to use quality components in all sub assemblies. Usually using an over-rated component, if available, can extend the life considerably. On the other hand, if you have control on the specific end use, you should focus on the various possible failure modes of the assembly.