I always wondered if that was because the British media are full of students of English, while the US is stuck with students of journalism (eg https://en.wikipedia.org/wiki/Journalistic_objectivity). The latter seems to correlate with a delusion of grandeur.

I disagree, whereas it is well-known that sections of the media has a bias which colours it's coverage, it is never explicitly declared and it also tends towards the dogmatic. I would be interested to see an example where this isn't the case.