Yes, those expecting people to announce the location of an NM and wait a few mins for people to gather are being entitled. Player A who found the boss is in no form of social contract to help others out, but they may choose to do so to help others who would benefit.

In the same way people who expect others not to let a door swing closed on them if they are a few paces behind are being entitled. Person A who has just walked through the door is in no form of social contract to help others out, but they may choose to do so to help others who would benefit.

In both cases, 'Person A' has an opportunity to help others at little personal cost. In neither case do they have to. In both cases the convention is that they should.

So don't be surprised if someone complains about NMs not being held, we complain when doors are allowed to close in our faces too. It's just manners.