> That's good PR, mentioning that Bezos owns WP when it is completely irrelevant, in order to foster a feeling of openness and honesty
It is standard practice, when a newspaper reports on its owner, for it to point out the fact of ownership. It is considered good journalistic ethics. It is reminding the readers of the possibility that their reporting on their owner might be prone to bias, even if there is no sign of bias in any particular case.
Here in Australia, every time The Sydney Morning Herald (Sydney's broadsheet) or The Age (Melbourne's broadsheet) mentions Nine Entertainment (the Australian TV network, and more recently owner of those newspapers), they add a parenthetical aside ("the owner of this masthead"). Different publications, different country, same principle.