This is my first reaction too, but then I must remember that it's free to publish in Nature (and Science, et. al.) because of their massive readership. I don't think they'll go anywhere for a long time, because people will always want a prestigious place to put their research.

It may be a combination of idealism (fostered by their status as the leading publisher, which while I haven't looked I would bet means they make a ton of money) and cold business logic that this hurts their competitors more than them.