Valuable point. I'm not sure if I agree with the "excellent value". However, at least ACM tries to be reasonably fair. Recently they seem to have introduced a clause in the copyright transfer from which allows you to retain copyright for specific figures in your paper. Still a far way from Open Access but way better than all other major publishers. What I really hate about publishers like Elsevier or Springer is that they claim to add value by ensuring only high-quality papers get published. In reality, every major publisher, except ACM, seems to be perfectly happy with publishing a lot of rubbish research.

(My favorite: El Naschie's photo gallery in Elsevier's Chaos, Solitons and Fractals: www.el-naschie.net/bilder/file/Photo-Gallery.pdf)