"To be perfectly clear, APA is operating well within their rights here– authors did sign an agreement granting APA copyright to their works..."
Yes. APA has the right to send the takedown notices. But will this move be of any benefit to them? What do they lose if an author places the final version of record of all her papers in her website? Do they really believe they have a big market for reprints (requests for single articles on payment)?
By sending such notices they will certainly lose goodwill among the authors. More importantly, why did they in the first place demand authors to surrender even this simple right when they sent out the copyright form?
It is moves such as these by publishers that give rise to the rise of sites like SciHub and then publishers indulge in breastbeating.
Subbiah Arunachalam