Because you don't just need to do it, someone on the other end needs to receive it. If every "ask" is met with annoyance, every debrief with "uh ok, still ready for september deadline?" and every warn with "but you promised! does this mean we will have to move the september deadline again?" then it's not hard to imagine people stop doing it.
His list implies a promise that he will not respond like this.
I think that is the intent too, but he really should spell out what his response will be to each of those things: "Ask", "Debrief", "Warn". The onus is on the manager to handle each mishap in a way helps the project and supports those doing the work.
In quite a lot of work environments, being a bearer of "bad news" will often lead to getting your head chewed off. A certain level of trust is absolutely required for workers to be truly frank with their project manager.
This was my thinking, too. We had a Lt in the air force that was fond of saying "if you have any concerns, come to me. my door is always open." The problem was that if you did that, your concerns were either blown off or interpreted as personal criticism.
The points made in the OP are good, but saying that is easy. It's when the deadlines start blowing by that the real test comes as to whether he can actually live up to it and not start backsliding.
His list implies a promise that he will not respond like this.