The point of the article is that sometimes they're not equivalent, and that creates a lot of confusion. Please read it before commenting on it.

Arrays and pointers are never equivalent. One is a clump of like-sized objects allocated consecutively; the other is a referential type indicating the location of an object or function.

I thought the same things as GP. Anyone who has read K&R (as any C programmer ought to have) will know everything in this article.

I don't think that's true. While I don't have my copy of K&R handy, I don't recall it covering all the subtleties of how assignment and increment operators and sizeof will work differently for something declared as an array vs. something declared as a pointer. At least in the edition I've had, it just had the same "pointers and arrays are equivalent" which is misleading in exactly the way this article describes. Did that get added in your much-later edition?

I'd go so far as to say that any C programmer at all (whether or not they've read K&R) will know everything in this article. However, it's probably interesting or useful for people who are either in the process of learning C, or people who have to read and write it occasionally, but never truly learned the language. These are definitely all pain points for people coming to C from higher-level languages.