In euphemism treadmill it looks like a word gets replaced because a secondary derogatory or offensive meaning of it comes to dominate with the general public and so the word in its original, often technical, use gets replaced.
E.g., "retarded" was originally a medical term, became a general purpose derogatory word, and then medicine switched to something else because of that.
In all the examples given on that page this replacement happens.
That's not what is happening in the AP guide changes. E.g., when they say don't use "the poor" they aren't saying to no longer use the word "poor". They are saying to say "poor people" or "people who are poor" instead of "the poor".
I don't see the difference between "the poor" and "people who are poor." As described in the cambridgeblog post, the problem is the underlying issue (e.g., being poor), not necessarily the phrases used to describe the issue.
I suppose you can say that, as time progresses, certain terms are saddled with unnecessary pejorative baggage (e.g., "retarded"), so I can understand the desire to swap in a new term that doesn't have the baggage. But sometimes it seems that the difference is so fine (e.g., between "the poor" and "poor people") that I don't have the resolving power to tell the difference.