Google leans pretty heavily on machine learning for even trivial design choices http://stopdesign.com/archive/2009/03/20/goodbye-google.html mentions the infamous testing of 41 shades of bue to decide which was the correct one.

But truly someone has to design the learning system, at some level you will always have design, if it is the design of how the design is to adapt to it's environment.

What's to say those spam websites aren't exactly that?

Well, this website modifies a lot of variables, though it doesn't make everything variable: http://www.metamorphosite.com/about