I'm sure David MacKay is well aware of the need for normalization — his point is that people use PCA without understanding what it means and how to perform it p

I'm sure David MacKay is well aware of the need for normalization — his point is that people use PCA without understanding what it means and how to perform it properly. Memorizing a technique without having any idea of why the technique works often leads to meaningless (or worse, incorrect) interpretations of data.