There is a difference between “not bothering the cleaning staff” and not acknowledging that they exist and are human and are standing right in front of you.
Author is describing the second, and it happens pervasively in the upper classes.
Sadly, this is true. Though it also leaves a huge opportunity for people to encourage cleaning staff (or drivers or any other manual labor in cultures that privilege intellectual work) with brief yet heartfelt greetings and genuine thanks for the valuable work they do.
Seeing and thanking overlooked people for the work they do takes almost no time if its habitual, yet can potentially brighten someone's day.
Author is describing the second, and it happens pervasively in the upper classes.