Take a look at the pages that are still up (which are for non-ACM conferences). They are a list of the proceedings, with links to freely available copies of all of the papers. Presumably, these papers are on the authors' websites.
Note that the ACM copyright form explicitly allows authors to put up a copy of their published paper on their own website. So, from what I can surmise, they requested he take down links to material that is freely and legally available.
Ah, I see. That does sound like the logical conclusion (and is just as icky as the poster suggests). But I'd still like to hear what basis ACM is using to, ah, "request" that the links be taken down.
Note that the ACM copyright form explicitly allows authors to put up a copy of their published paper on their own website. So, from what I can surmise, they requested he take down links to material that is freely and legally available.