HPSOV L:
Actually the Qantas 380 Captain out of SIN used a PAN call. Later stating "at no time did I feel our lives were in danger".
But you are providing an example of a quad loosing an engine, not a twin.
In the example you provide multiple systems of each type remain functioning.
In the twin scenario, 50% of some systems are gone, a single source remains, hence the MayDay is warranted whereas in the case of a quad a simple PAN will suffice