I once came across a landing page for a well known (to the HN crowd, at least) that claimed us as a customer, even though we weren't using the products they were advertising us on. It took a month or so for them to remove it, and since then I've been a lot more cynical about what I see there.
Real question: How much do you think young start-ups pay majors to add their name to the 'trusted by' sections? For me, it feels like paid adverts in search results. I always ignore/discount them. That said, 'trusted by' sections are targeting The Suits (CTOs, etc.), not hands-on folks like me.
They're targeting the marketing person that put them there because the landing page template they bought to customize had such a section. Nobody gets paid anything for it.