I don't think you understand pg's piece or how PR works. The idea is that the article is there because it was pitched by a PR agency rather than the journalist sniffing it out. The grain of sand that creates the pearl is from the PR agency. There's not a corrupt payment; the client pays the PR company, the PR company doesn't pay the publication. The PR company and their client don't need to offer a corrupt payment because they are giving the publication something useful - an easy start on an article - but it's at the editor's discretion whether it makes it to the audience.
A newspaper/magazine/site wants to fill pages with things of interest. Sometimes it's investigative (though often these are built through tip-offs anyway), sometimes it's fluffier. The PR company is briefed by the client and then develops things to pitch that suit a particular publication. They build these relationships over time and don't want to destroy them with consistently bad story pitches. PG's article goes through this.
If there's a business person profiled on the front of the careers liftout, that was the work of their PR company. PG estimated half of the news, but I'd guess it to be higher than that. Once you've seen behind the scenes, you recognise it in almost every article.
I didn't read this Metallica article, but the client could've been Metallica, the venue, or something else. If there are quotes from Metallica, that will almost certainly tell you it was them. The writer doesn't need payment from the client or PR company because they are being handed an interview opportunity on a platter, or exclusive quotes or convinced that some other element of the angle will be of interest to their readers (stage configuration, etc).