I interpret this kind of thing to just mean the health benefits of being "not sedentary" relative to "sedentary" are pretty large. There is no magic number of steps nor is it the case that walking has magic benefits relative to other forms of exercise, it's just that it's a decent measure of "doing something" regularly versus "not."
The important issue for the US, especially, is that if you live in a car-based suburb - a place where your daily needs have to be met by driving, and so all walking is a separate deliberate choice - getting those "steps" is difficult.
On days I don't do anything in particular except leave the house to go to the supermarket and maybe grab a coffee, I probably clock 4500 steps. That's time I would spend in a car if I lived elsewhere.
