There's something very weird about this. I'm surprised that they would post this in the Kindle forums, and the tone is just odd:

We want you to know that ultimately, however, we will have to capitulate and accept Macmillan's terms because Macmillan has a monopoly over their own titles, and we will want to offer them to you even at prices we believe are needlessly high for e-books.

If that's true, then why wait? Just "capitulate" now and get it over with. If you're going to tell the other side that you're going to cave anyway, you've pretty much given up all bargaining power.

I see the move to this agency model as such a monumentally bad deal for Amazon that it seems like one of four things must be going on here:

   a) They've analyzed the situation and know they can't win (unlikely)
   b) There's a legal reason that they can't do what they're doing (unlikely)
   c) They're running a more elaborate play than we all realize
   d) This was posted in error or without authorization