It's exclusive to non-American, ie, doing this "always marketing yourself" thing whenever you talk or write or communicate in any way is kinda exclusive to Americans (as being acceptable and normal). The "sell yourself" culture is pretty deeply ingrained in this country in almost all personal communication, except with very close and trusted friends, and even then you'll often find inclinations to sell themselves socially.
I think your armchair anthropology ignores the diversity of speakers and cultures in the United States. Could you share more about your methodology?
Also, the OP _is_ selling something. If you opened your eyelids slightly, you could see his mentioning of an online ‘course.’ This article is itself “content marketing” so the OP is likely fishing for customers from this HN post.
Checking OP's posting history, it appears to be all his own articles/blog posts/whatever. Yep, shameless self-promoting spammer. That's enough to guarantee I will not be reading (let alone purchasing) anything from him.
