One of the READMEs specifically promised that the manager believes their paid job is to adapt to their reports' style, so, no.
(I mean, that sounds like a good thing. Firing people who aren't good for the team is an important responsibility of any manager who doesn't want the rest of their team to quit, so I would ideally want to know that my manager has at least thought about it a little.)
My understanding is that Netflix intends to have an unusually high-firing culture (cf. their culture deck, "The unusual part is that we give adequate performers a generous severance package"), so if I'm at Netflix I absolutely want my manager to be up-front about how they interpret that and what signs I have that I'm an adequate performer and not a top one. By signing onto Netflix I am afraid of being fired, but that reflects on the company and not on the manager. (And the answers this manager gave are good: statistics about firing and an explicit statement that it won't take you by surprise.) You'll note that the firing talk is gone from the current version, and the green/yellow/red performance stuff (which is generically useful) stays.
Referring to the Netflix version of the slide deck as "the old version" of the Slack version of the slide deck is inaccurate. I'm in a somewhat unusual position amongst the people whose READMEs were quoted, because I got to write one from both sides of the fence: As the established person welcoming a new member to the team (Netflix), and as someone joining a new organization (Slack). READMEs, for me, then end up looking very different.
It's also worth noting, as geofft notes, that Slack's culture and Netflix's culture are very very different, so the concerns of people within them would be different (and should be addressed differently). The concern that you might be fired was pervasive for new people at Netflix, and I sought to alleviate it; it's not a commonly-held concern at Slack.